Efficient rach behavior

ABSTRACT

Apparatuses, methods, and systems are disclosed for efficient RACH behavior. One apparatus includes a transmitter that transmits a first PRACH preamble to a base unit to start a RACH procedure; a receiver that receives a RAR (Msg2) from the base unit during a random access response window; and a processor that controls the transmitter to transmit a second PRACH preamble in response to being unable to transmit a RACH Msg3 within an indicated transmission opportunity. The processor may obtain multiple transmission opportunities for transmitting a RACH message such as RACH Msg1 or RACH Msg3 or monitor for multiple RACH Msg2 where transmission opportunity data are conveyed via a RACH Order, an RAR, or DCI for the RACH message. A method or system may perform functions of the apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application Ser. No.62/692,542 entitled “RACH BEHAVIOR FOR NR-U” and filed on Jun. 29, 2018for Alexander Golitschek Edler Von Elbwart, Prateek Basu Mallick,Joachim Loehr, Hyejung Jung, and Vijay Nangia, which is incorporatedherein by reference in its entirety.

FIELD

The subject matter disclosed herein relates generally to wirelesscommunications and more particularly relates to an efficient RACHbehavior, such as for NR-U.

BACKGROUND

The following abbreviations are herewith defined, at least some of whichare referred to within the following description: Third GenerationPartnership Project (“3GPP”), Fifth Generation Core Network (“5CG”),Fifth Generation System (“5GS”), Access and Mobility Management Function(“AMF”), Positive-Acknowledgment (“ACK”), Access Stratum (“AS”),Automatic Repeat Request (“ARQ”), Autonomous UpLink (“AUL”), BackoffIndicator (“BI”), Base Station (“BS”), Binary Phase Shift Keying(“BPSK”), Bandwidth Part (“BWP”), Cell Radio Network TemporaryIdentifier (“C-RNTI”), Clear Channel Assessment (“CCA”), Cyclic Prefix(“CP”), Cyclical Redundancy Check (“CRC”), Channel State Information(“CSI”), Common Search Space (“CSS”), Connection Mode (“CM”, this is aNAS state in 5GS), Contention Based Random Access (“CBRA”), ContentionFree Random Access (“CFRA”), Control Plane (“CP”), Core Network (“CN”),Data Radio Bearer (“DRB”), Discrete Fourier Transform Spread (“DFTS”),Downlink Control Information (“DCI”), Downlink (“DL”), Downlink PilotTime Slot (“DwPTS”), Discontinuous Transmission (“DTX”), DualConnectivity (“DC”), Dual Registration mode (“DR mode”), Enhanced ClearChannel Assessment (“eCCA”), Enhanced Licensed Assisted Access (“eLAA”),Enhanced Mobile Broadband (“eMBB”), Evolved Node-B (“eNB”), EvolvedPacket Core (“EPC”), Evolved Packet System (“EPS”), EPS MobilityManagement (“EMM”) (this is a NAS state in EPS), Evolved UMTSTerrestrial Radio Access (“E-UTRA”), European TelecommunicationsStandards Institute (“ETSI”), Frame Based Equipment (“FBE”), FrequencyDivision Duplex (“FDD”), Frequency Division Multiple Access (“FDMA”),Frequency Division Orthogonal Cover Code (“FD-OCC”), Guard Period(“GP”), Globally Unique Temporary UE Identifier (“GUTI”), HybridAutomatic Repeat Request (“HARQ”), Internet-of-Things (“IoT”),International Mobile Subscriber Identity (“IMSI”), Licensed AssistedAccess (“LAA”), Load Based Equipment (“LBE”), Listen-Before-Talk(“LBT”), Long Term Evolution (“LTE”), Multiple Access (“MA”), MediumAccess Control (“MAC”), Mobility Management Entity (“MME”), ModulationCoding Scheme (“MCS”), Machine Type Communication (“MTC”), MultipleInput Multiple Output (“MIMO”), Multi User Shared Access (“MUSA”),Narrowband (“NB”), Negative-Acknowledgment (“NACK”) or (“NAK”), NewGeneration Node B (“gNB”), New Generation Radio Access Network(“NG-RAN”, a RAN used for 5GS networks), New Radio (“NR”), New Radio inUnlicensed Spectrum (“NR-U”), Non-Access Stratum (“NAS”), Non-OrthogonalMultiple Access (“NOMA”), Normal Uplink (“NUL”), Operation andMaintenance System (“OAM”), Orthogonal Frequency Division Multiplexing(“OFDM”), Packet Data Unit (“PDU”) (used in connection with ‘PDUSession’), Packet Switched (“PS”, e.g., Packet Switched domain or PacketSwitched service), Primary Cell (“PCell”), Physical (“PHY”), PhysicalBroadcast Channel (“PBCH”), Physical Downlink Control Channel (“PDCCH”),Physical Downlink Shared Channel (“PDSCH”), Pattern Division MultipleAccess (“PDMA”), Physical Hybrid ARQ Indicator Channel (“PHICH”),Physical Random Access Channel (“PRACH”), Physical Resource Block(“PRB”), Physical Uplink Control Channel (“PUCCH”), Physical UplinkShared Channel (“PUSCH”), Public Land Mobile Network (“PLMN”), Qualityof Service (“QoS”), Quadrature Phase Shift Keying (“QPSK”), Radio AccessNetwork (“RAN”), Radio Access Technology (“RAT”), Radio Resource Control(“RRC”), Random Access Procedure (“RACH”), Random Access Response(“RAR”), Radio Network Temporary Identifier (“RNTI”), Random AccessRadio Network Temporary Identifier (“RA-RNTI”), Reference Signal (“RS”),Registration Area (“RA”) (similar to tacking area list used in LTE/EPC),Registration Management (“RA”, refers to NAS layer procedures andstates), Remaining Minimum System Information (“RMSI”), Resource SpreadMultiple Access (“RSMA”), Round Trip Time (“RTT”), Receive (“RX”),Sparse Code Multiple Access (“SCMA”), Scheduling Request (“SR”), SingleCarrier (“SC”), Single Carrier Frequency Division Multiple Access(“SC-FDMA”), Secondary Cell (“SCell”), Shared Channel (“SCH”), SessionManagement Function (“SMF”), Signal-to-Interference-Plus-Noise Ratio(“SINR”), Single Network Slice Selection Assistance Information(“S-NSSAI”), Single Registration mode (“SR mode”), System Frame Number(“SFN”), System Information Block (“SIB”), Synchronization Signal(“SS”), Supplementary Uplink (“SUL”), Tracking Area (“TA”), TechnicalSpecification (“TS”), Transport Block (“TB”), Transport Block Size(“TBS”), Time-Division Duplex (“TDD”), Time Division Multiplex (“TDM”),Time Division Orthogonal Cover Code (“TD-OCC”), Transmission TimeInterval (“TTI”), Transmit (“TX”), Unified Data Management (“UDM”),Uplink Control Information (“UCI”), User Entity/Equipment (MobileTerminal) (“UE”), Uplink (“UL”), User Plane (“UP”), Universal MobileTelecommunications System (“UMTS”), UMTS Terrestrial Radio Access(“UTRA”), UMTS Terrestrial Radio Access Network (“UTRAN”), Uplink PilotTime Slot (“UpPTS”), Ultra-reliability and Low-latency Communications(“URLLC”), and Worldwide Interoperability for Microwave Access(“WiMAX”). As used herein, “HARQ-ACK” may represent collectively thePositive Acknowledge (“ACK”) and the Negative Acknowledge (“NACK”). ACKmeans that a TB is correctly received while NACK (or NAK) means a TB iserroneously received.

When there is a handover of a UE from a source cell to a target cell inNew Radio in Unlicensed Spectrum (“NR-U”), according to the RACHprocedure after the preamble transmission (PRACH, Msg1) the UE expects aRandom Access Response (RAR, Msg2), which among other informationincludes the Random Access Response Grant indicating transmissionparameters related to the following UE's transmission (Msg3). All thesetransmissions happen on the unlicensed medium, which may imply a need tofollow a Listen-Before-Talk (“LBT”) procedure for each of those messagesindividually and independently. Specifically, the Grant transmitted inMsg2 for Msg3 includes a timing offset, e.g., indicating a specific timeslot in which the UE is to transmit Msg3.

The successful reception of Msg3 may fail (from the base unit'sperspective) due to the following reasons: 1) The UE was not able todetect Msg2 successfully, caused by noise or interference by (e.g.hidden) nodes; or 2) The UE was not able to access the channel for Msg3transmission in the indicated time slot due to LBT failure (unsuccessfulCCA); or 3) The base unit was not able to detect Msg3 successfully,caused by noise or interference by (e.g. hidden) nodes.

Existing solutions enable the base unit to request a HARQ retransmissionof Msg3, i.e., follow the established HARQ procedure for Msg3. Whilerequesting a HARQ retransmission may remedy Reasons 2 and 3 above,requesting a HARQ retransmission does not remedy Reason 1. This isbecause the UE is not even aware what kind of transport block isrequested for retransmission. Following the HARQ procedure implies adelay, caused by the additional round-trip time of transmitting the HARQretransmission request by the base unit, and the followingretransmission by the UE—both of which may suffer additional delaycaused by the required LBT procedure for both these transmissions. Referto 3GPP TS 38.321 v15.2.0.

According to existing solutions, Reason 1 can only be rectified afterthe random access response window has expired, a preamble transmissioncounter is incremented, and the whole procedure continues with the UEtransmitting Msg1 again. Waiting for the random access response windowto expire and then continuing with the UE transmitting Msg1 again alsoimplies a delay for the successful completion of the overall randomaccess procedure.

BRIEF SUMMARY

Apparatuses, methods, and systems are disclosed for performing anefficient RACH procedure. A method is disclosed that includestransmitting a first physical random-access channel (“PRACH”) preambleto a base unit to start a RACH procedure; receiving a random accessresponse from the base unit during a random access response window; andtransmitting a second PRACH preamble in response to being unable totransmit a RACH Msg3 within an indicated RACH Msg3 transmissionopportunity.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the embodiments briefly described abovewill be rendered by reference to specific embodiments that areillustrated in the appended drawings. Understanding that these drawingsdepict only some embodiments and are not therefore to be considered tobe limiting of scope, the embodiments will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of awireless communication system for efficient RACH behavior;

FIG. 2 is a schematic block diagram illustrating one embodiment of auser equipment apparatus that may be used for efficient RACH behavior;

FIG. 3 is a schematic block diagram illustrating one embodiment of abase unit apparatus that may be used for efficient RACH behavior;

FIG. 4 is a block diagram illustrating one embodiment of a RACHprocedure;

FIG. 5 is a block diagram illustrating one embodiment of an efficientRACH behavior;

FIG. 6 is a block diagram illustrating another embodiment of anefficient RACH behavior;

FIG. 7 is a block diagram illustrating a further embodiment of anefficient RACH behavior; and

FIG. 8 is a schematic block diagram illustrating one embodiment of amethod for performing a RACH procedure with an efficient RACH behavior.

DETAILED DESCRIPTION

As may be appreciated by one skilled in the art, aspects of theembodiments may be embodied as a system, apparatus, method, or programproduct. Accordingly, embodiments may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,embodiments may take the form of a program product embodied in one ormore computer readable storage devices storing machine readable code,computer readable code, and/or program code, referred hereafter as code.The storage devices may be tangible, non-transitory, and/ornon-transmission. The storage devices may not embody signals. In acertain embodiment, the storage devices only employ signals foraccessing code.

Any combination of one or more computer readable medium may be utilized.The computer readable medium may be a computer readable storage medium.The computer readable storage medium may be a storage device storing thecode. The storage device may be, for example, but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, holographic,micromechanical, or semiconductor system, apparatus, or device, or anysuitable combination of the foregoing.

More specific examples (a non-exhaustive list) of the storage devicewould include the following: an electrical connection having one or morewires, a portable computer diskette, a hard disk, a random-access memory(“RAM”), a read-only memory (“ROM”), an erasable programmable read-onlymemory (“EPROM” or Flash memory), a portable compact disc read-onlymemory (“CD-ROM”), an optical storage device, a magnetic storage device,or any suitable combination of the foregoing. In the context of thisdocument, a computer readable storage medium may be any tangible mediumthat can contain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

Code for carrying out operations for embodiments may be any number oflines and may be written in any combination of one or more programminglanguages including an object-oriented programming language such asPython, Ruby, Java, Smalltalk, C++, or the like, and conventionalprocedural programming languages, such as the “C” programming language,or the like, and/or machine languages such as assembly languages. Thecode may execute entirely on the user's computer, partly on the user'scomputer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (“LAN”) or a wide area network (“WAN”), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider).

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. Thus, appearances of the phrases“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment, but mean “one or more but not all embodiments” unlessexpressly specified otherwise. The terms “including,” “comprising,”“having,” and variations thereof mean “including but not limited to,”unless expressly specified otherwise. An enumerated listing of itemsdoes not imply that any or all of the items are mutually exclusive,unless expressly specified otherwise. The terms “a,” “an,” and “the”also refer to “one or more” unless expressly specified otherwise.

Furthermore, the described features, structures, or characteristics ofthe embodiments may be combined in any suitable manner. In the followingdescription, numerous specific details are provided, such as examples ofprogramming, software modules, user selections, network transactions,database queries, database structures, hardware modules, hardwarecircuits, hardware chips, etc., to provide a thorough understanding ofembodiments. One skilled in the relevant art will recognize, however,that embodiments may be practiced without one or more of the specificdetails, or with other methods, components, materials, and so forth. Inother instances, well-known structures, materials, or operations are notshown or described in detail to avoid obscuring aspects of anembodiment.

Aspects of the embodiments are described below with reference toschematic flowchart diagrams and/or schematic block diagrams of methods,apparatuses, systems, and program products according to embodiments. Itwill be understood that each block of the schematic flowchart diagramsand/or schematic block diagrams, and combinations of blocks in theschematic flowchart diagrams and/or schematic block diagrams, can beimplemented by code. The code may be provided to a processor of ageneral-purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions/acts specified in the schematic flowchartdiagrams and/or schematic block diagrams block or blocks.

The code may also be stored in a storage device that can direct acomputer, other programmable data processing apparatus, or other devicesto function in a particular manner, such that the instructions stored inthe storage device produce an article of manufacture includinginstructions which implement the function/act specified in the schematicflowchart diagrams and/or schematic block diagrams block or blocks.

The code may also be loaded onto a computer, other programmable dataprocessing apparatus, or other devices to cause a series of operationalsteps to be performed on the computer, other programmable apparatus, orother devices to produce a computer implemented process such that thecode which execute on the computer or other programmable apparatusprovide processes for implementing the functions/acts specified in theflowchart and/or block diagram block or blocks.

The schematic flowchart diagrams and/or schematic block diagrams in theFigures illustrate the architecture, functionality, and operation ofpossible implementations of apparatuses, systems, methods, and programproducts according to various embodiments. In this regard, each block inthe schematic flowchart diagrams and/or schematic block diagrams mayrepresent a module, segment, or portion of code, which includes one ormore executable instructions of the code for implementing the specifiedlogical function(s).

It should also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in theFigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. Other steps and methods may be conceived that are equivalentin function, logic, or effect to one or more blocks, or portionsthereof, of the illustrated Figures.

Although various arrow types and line types may be employed in theflowchart and/or block diagrams, they are understood not to limit thescope of the corresponding embodiments. Indeed, some arrows or otherconnectors may be used to indicate only the logical flow of the depictedembodiment. For instance, an arrow may indicate a waiting or monitoringperiod of unspecified duration between enumerated steps of the depictedembodiment. It will also be noted that each block of the block diagramsand/or flowchart diagrams, and combinations of blocks in the blockdiagrams and/or flowchart diagrams, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts, or combinations of special purpose hardware and code.

The description of elements in each figure may refer to elements ofproceeding figures. Like numbers refer to like elements in all figures,including alternate embodiments of like elements.

As used herein, a list with a conjunction of “and/or” includes anysingle item in the list or a combination of items in the list. Forexample, a list of A, B and/or C includes only A, only B, only C, acombination of A and B, a combination of B and C, a combination of A andC or a combination of A, B and C. As used herein, a list using theterminology “one or more of” includes any single item in the list or acombination of items in the list. For example, one or more of A, B and Cincludes only A, only B, only C, a combination of A and B, a combinationof B and C, a combination of A and C or a combination of A, B and C. Asused herein, a list using the terminology “one of” includes one and onlyone of any single item in the list. For example, “one of A, B and C”includes only A, only B or only C and excludes combinations of A, B andC. As used herein, “a member selected from the group consisting of A, B,and C,” includes one and only one of A, B, or C, and excludescombinations of A, B, and C.” As used herein, “a member selected fromthe group consisting of A, B, and C and combinations thereof” includesonly A, only B, only C, a combination of A and B, a combination of B andC, a combination of A and C or a combination of A, B and C.

Generally, the present disclosure describes systems, methods, andapparatus that provide efficient RACH behavior for a scenario where atransmission of at least one RACH message may fail due to radio resourceaccess rule(s), such as for NR-U. In some embodiments, multipletransmission opportunities are supported for RACH Msg1, RACH Msg2, andRACH Msg3 to alleviate the transmission restrictions imposed by LBT anddelay caused by Msg3 retransmissions according to the HARQ protocol. Invarious embodiments, any RACH behavior or portion thereof may beconsidered efficient if it minimizes one or more delays relative todelays which may occur with an unmodified RACH behavior found in anexisting standard such as found in Release 15.

It may be noted that the present disclosure uses terminology to describevarious messages and procedures as outlined in 3GPP LTE, NR, and/or NR-Uspecifications available at the time of filing. Specifically, for theRandom Access Procedure (sometime called RACH Procedure). FIG. 4 showsfrequently used NR and/or NR-U terminology for the four involved messageexchanges. Note that in the NR or NR-U context, the terms “gNB”, or “RANnode” may be used instead of “base unit.”

It may be noted that FIGS. 4-7 depict a so-called “contention-basedrandom access” (CBRA). However, the present disclosure may also beapplied to “contention-free random access” (CFRA), for which somedetails are given later. Likewise, the principles of the solutions andembodiments may be applied to a 2-step RACH procedure, where only twomessages are exchanged.

A first embodiment to support an efficient RACH behavior, such as forNR-U (e.g., multiple transmission occasions for RACH Msg2 and RACH Msg3)includes changing the UE behavior to monitor the DL control channel forMsg2 transmissions even after it has successfully received a RandomAccess Response containing Random Access Preamble identifiers thatmatches the transmitted PRACH preamble, i.e., even after the RandomAccess Response (Msg2) reception is considered successful.

Moreover, to avoid conflicting or unclear behavior with respect to theMsg3 transmission, the UE may expect that multiple Msg2 transmissionsindicate the same Msg3 transport block parameters, such that thetransport block size indicated by two (or more) Msg2 transmissionswithin the ra-ResponseWindow does not change. This simplifies the UEimplementation because the same data payload can be kept in thetransmission buffer. This efficient UE behavior allows the base unit toperform multiple Msg2 transmissions to the same UE within thera-ResponseWindow. Note that from the lack of successful Msg3 reception(e.g., by DTX detection on Msg3 PUSCH resource or associated referencesignal corresponding to Msg3), the base unit cannot know whether the UEfailed to receive a Msg2 transmission, or whether channel access was notallowed due to a failed LBT.

According to current specification, in the case where the UE has missedMsg2 reception, the UE continues to monitor for PDCCH with CRC scrambledby RA-RNTI until the end of the ra-ResponseWindow until it receives avalid PDCCH with CRC scrambled by RA-RNTI and the Random Access Responsecontaining Random Access Preamble identifier that matches thetransmitted PRACH preamble index. Therefore, the base unit cannot besure whether a HARQ retransmission grant will be interpreted correctlyby the UE, as the UE's correct interpretation of the retransmissiongrant requires a successful reception of Msg2 addressed to the UE. Invarious embodiments, the UE is instructed to continue monitoring forRandom Access Responses (Msg2) for the whole duration of thera-ResponseWindow.

Note that, according to the existing specification, monitoring forRandom Access Responses (Msg2) for the whole duration of thera-ResponseWindow implies monitoring downlink control information (DCI)where the CRC parity bits are scrambled with the RA-RNTI. With thisembodiment, the base unit can send another Msg2 (with the mentionedconstraint of the transport block size), where the CRC parity bits ofthe DCI are scrambled with a Temporary Cell-Radio Network TemporaryIdentifier (TC-RNTI) or scrambled with a Cell-Radio Network TemporaryIdentifier (C-RNTI), to schedule another Msg3 opportunity, instead ofusing a PDCCH carrying DCI triggering a HARQ retransmission of Msg3. Ina further enhancement of the first embodiment, the Msg2 may include anadditional redundancy version (RV) parameter to facilitate efficientHARQ combination of different Msg3 transmissions.

In certain embodiments, the UE may restart the RACH response window,i.e. ra-ResponseWindow, upon having successfully received a RAR for thecorresponding PRACH preamble transmission, i.e. considering the RandomAccess Response reception successful, thereby dynamically extending thetime during which a UE monitors for a PDCCH carrying DCI where the CRCparity bits of the DCI are scrambled with RA-RNTI. Such an approach issuited to the case that the UE has received the RAR successfully, butwas unable to transmit the Msg3 e.g., due to a blocked channel at theindicated time.

In the embodiments and enhancements described, the ra-ResponseWindow orthe total time during which the UE monitors for Msg2 PDCCH carrying DCIwhere the CRC parity bits of the DCI are scrambled with RA-RNTI(including any restart of the RACH response window) may need to beincreased/extended. This may result in a Msg2 (RAR) window length thatis greater than 10 ms (a radio frame or system frame), note that 10 msis the current maximum value for Msg2 (RAR) window length according tocurrent specification. To uniquely identify the multiple RACH occasionswith the larger (>10 ms) Msg2 window, the RA-RNTI computation may needto be updated and/or be based on the SFN (System Frame Number). Incertain embodiments, the RA-RNTI may be based on an integer parameter‘x’ representing the maximum allowed value of the (extended) Msg2 window(ra-ResponseWindow) (e.g., in multiple of 10 ms) which may be fixed inthe specification (e.g., x=ceiling(max Msg2 window length (in ms)/10),where ceiling(num)=the smallest integer equal to or greater than num, sox=2 for 20 ms, e.g., a maximum value of the Msg2 window) or signaled viahigher layers such as in the RACH configuration.

In one embodiment, defining the extended Msg2 window may be realized bythe defining the RA-RNTI associated with the PRACH in which the RandomAccess Preamble is transmitted as:

RA-RNTI=1+s_id+14×t_id+14×8×f_id+14×80×8×ul_carrier_id+14×80×8×2×SFN modx   Eq. 1

where s_id is the index of the first OFDM symbol of the specified PRACH(0≤s_id<14), t_id is the index of the first slot of the specified PRACHin a system frame (0≤t_id<80), f_id is the index of the specified PRACHin the frequency domain (0≤f_id<8), SFN is the system frame number ofthe specified PRACH, ‘x’ is the maximum allowed value of thera-ResponseWindow, and ul_carrier_id is the UL carrier used for Msg1transmission (0 for NUL carrier, and 1 for SUL carrier).

Alternatively, defining the extended Msg2 window may be realized bydefining the RA-RNTI associated with the PRACH in which the RandomAccess Preamble is transmitted as:

RA-RNTI=1+s_id+14×t_id+14×80×f_id+14×80×8×SFN modx+14×80×8×x×ul_carrier_id   Eq. 2

where s_id is the index of the first OFDM symbol of the specified PRACH(0≤s_id<14), t_id is the index of the first slot of the specified PRACHin a system frame (0≤t_id<80), f_id is the index of the specified PRACHin the frequency domain (0≤f_id<8), SFN is the system frame number ofthe specified PRACH, ‘x’ is the maximum allowed value of thera-ResponseWindow, and ul_carrier_id is the UL carrier used for Msg1transmission (0 for NUL carrier, and 1 for SUL carrier).

In a second embodiment, the UE may stop monitoring for Random AccessResponses (Msg2) as soon as Msg3 has been physically transmitted inresponse to Msg2 within the ra-ResponseWindow. In this regard, atransmission implies that CCA succeeded for Msg3, however it doesn'tnecessarily imply that the base unit has received the transmissionsuccessfully. In other words, the UE may stop monitoring for RandomAccess Responses (Msg2) if the physical layer indicates that Msg3 hasbeen transmitted. In this way, if Msg2 is received but CCA for Msg3fails, the UE still monitors for later Msg2 transmissions until thera-ResponseWindow stops. The effect is similar to the first embodiment:the base unit can send another Msg2 (with the mentioned constraint ofthe transport block size) to schedule another Msg3 opportunity, insteadof using a PDCCH carrying DCI where the CRC is scrambled withC-RNTI/TC-RNTI triggering a HARQ retransmission of Msg3. In a furtherenhancement of this embodiment, Msg2 includes an additional redundancyversion (RV) parameter to facilitate efficient HARQ combination ofdifferent Msg3 transmissions.

In various implementations, the MAC entity behavior may be defined asfollows to cover the second embodiment: The MAC entity may stopra-ResponseWindow (and hence monitoring for Random Access Response(s))after the physical layer indicates a transmission of RACH Msg3.Alternatively, the MAC entity behavior may be defined as stoppingra-ResponseWindow (and hence monitoring for Random Access Response(s))after the CCA for Msg3 transmission has succeeded.

Instead or in addition of using the physical layer transmission of Msg3as a stopping criterion of ra-ResponseWindow, one or more of thefollowing may be used to trigger stopping ra-ResponseWindow: Receptionof L2 ACK by UE, where the L2 ACK relates to the successful reception ofMsg3 by a base unit; Reception of a PDCCH carrying DCI where the CRC isscrambled with C-RNTI/TC-RNTI requesting a HARQ retransmission of Msg3;and Reception of Msg4 by the UE.

In a third embodiment, the Random Access procedure is continued with anew preamble transmission (Msg1), from the same preamble group as theprevious preamble transmission, in case the physical layer is not ableto transmit Msg3 in the indicated time slot. The third embodimentshortens the delay until continuing the RACH procedure with selectingand transmitting a PRACH preamble. This may be realized by consideringthe contention resolution timer ra-ContentionResolutionTimer as expiredin case the physical layer is not able to transmit Msg3 in the indicatedtime slot, e.g. due to a failed CCA. Alternatively, the third embodimentmay be realized by considering the Random Access procedure as ongoing orcontinuing in case the physical layer is not able to transmit Msg3 inthe indicated time slot. In an enhancement, the HARQ buffer used fortransmission of the MAC PDU in the Msg3 buffer may be flushed.

In case the UE has obtained multiple opportunities for Msg3transmission, in an alternative to the third embodiment the RandomAccess procedure is continued with a new preamble transmission (Msg1)from the same preamble group as the previous preamble transmission incase the physical layer is not able to transmit Msg3 in any of theindicated transmission opportunities (e.g., time slots). According tothis alternative, the MAC entity considers the Random Access procedureas ongoing or continuing if Msg3 could not be transmitted by thephysical layer, e.g. due to a failed CCA, in any of the time slot(s)indicated by Msg2. In certain embodiments, the HARQ buffer used fortransmission of the MAC PDU in the Msg3 buffer may be flushed if the UEcontinues the Random Access procedure with a new preamble.

In a further variant for the case that the UE receives multiple Msg2transmissions, the MAC entity considers the Random Access procedure asongoing or continuing if Msg3 could not be transmitted by the physicallayer, e.g. due to a failed CCA, in any of the time slot(s) indicated bythe plurality of Msg2 transmissions received during ra-ResponseWindow.This may be realized by considering the contention resolution timerra-ContentionResolutionTimer as expired in case the physical layer isnot able to transmit Msg3 in any of the indicated transmissionopportunities (e.g., time slots). Alternatively, it may be realized byconsidering the Random Access procedure as ongoing or continuing in casethe physical layer is not able to transmit Msg3 in any of the indicatedtime slots. In an enhancement, the Msg3 HARQ buffer is flushed if the UEcontinues the Random Access procedure with a new preamble.

In certain implementations, the UE continues with retransmission(s) ofthe preamble in case the physical layer is not able to transmit Msg3 inany of the indicated time slot(s), e.g. due to failed CCA. In anenhancement, the HARQ buffer used for transmission of the MAC PDU in theMsg3 buffer is flushed, and the transmit power of the preamble may beincreased. In one alternative, the transmission power is increased by apower ramping step size larger than that the configured power rampingstep size to be used if the UE did not receive any Msg2 transmission.The power ramping step size can be a predetermined or signaled offset tothe configured power ramping step size or correspond to the configuredpower-ramping step size for case of differentiated Random Accessprocedure (powerRampingStepHighPriority parameter).

According to the third embodiment and its alternatives and variants, anyretransmission of a preamble, or transmission of a new preamble as aresult of the physical layer not being able to transmit Msg3 in theindicated time slot or any of the indicated time slots, is beneficiallydone with no applied backoff, even if a backoff had been indicated in aMsg2, in order to not introduce additional delay. Alternatively, thebackoff value is reduced by scaling the backoff value by a predeterminedor signaled scaling factor (e.g., such as the Scaling factor for thebackoff indicator (BI) scalingFactorBI parameter) for prioritizing thepreamble transmission.

According to a further variant of the third embodiment, a UE maycontinue monitoring for a retransmission request of Msg3, i.e. PDCCHaddressed to either C-RNTI or TC-RNTI, in case the physical layer is notable to transmit Msg3 in any of the indicated time slot(s), whileperforming a (re)transmission of a PRACH preamble. The contentionresolution timer ra-ContentionResolutionTimer, started when the MAC PDUcontaining Msg3 was delivered from the MAC layer to the PHY layer fortransmission, may be still running while UE is (re)transmitting PRACHpreamble. For the case that the UE receives a PDCCH requesting aretransmission of Msg3, the UE may stop further transmission(s) of thePRACH preamble and potentially related monitoring for a correspondingRAR. Upon successful reception of a RAR for the preamble(re)transmission, UE may stop the contention resolution timer andcontinue with Msg3 transmission according to the received RAR.

A fourth embodiment provides for the transmission of Msg3 in one ofmultiple time slots (or multiple transmission occasions). Thisembodiment offers multiple transmission opportunities since the UE willhave several time slots for which LBT may allow channel access. To thisend, Msg2 includes a new “number of Msg3 time slots” (or “number of Msg3transmission occasions”) parameter indicating the number of time slots(or transmission occasions) in which the UE may transmit Msg3. Thesetime slots (or transmission occasions) may be consecutive ordistributed, which may also be configured by Msg2.

In one example, Msg2 may indicate a time slot (or transmission occasion)pattern during which Msg3 transmissions are authorized. In anotherexample, the number of potential Msg3 transmission occasions may beindicated to the UE via broadcast system information or dedicatedhigher-layer (i.e. RRC) signaling, or it is predefined in thespecification. The uplink grant field of MAC payload for Random AccessResponse (RAR) may include one or more Msg3 PUSCH time resourceallocation fields (e.g. multiples of 4 bits). The UE determines the sizeof MAC RAR based on the indicated or predetermined number of potentialMsg3 transmission occasions.

In one example, the UE is configured with a set of number of potentialMsg3 transmission occasions by higher layers (e.g., RRC) and the RARindicates one value from the set the UE should use for determining theindicated Msg3 transmission occasions. In another example, the UE alsoreceives an indication of an offset or gap value between consecutiveMsg3 transmission occasions in Msg2 RAR or configured by higher layersfor determining the indicated Msg3 transmission occasions. In anothervariant, the UE may be configured with a set of offset or gap values andnumber of potential Msg3 transmission occasion pairs by higher layers(e.g., RRC) and the Msg2 RAR indicates one value from the set the UEshould use for determining the indicated Msg3 transmission occasions. Inone variant, the UE may assume the Msg3 PUSCH time and frequencyresource allocation is the same in all the indicated Msg3 transmissionoccasions. If the clear channel assessment succeeds for any of theindicated time slots (or transmission occasions), the UE performs asingle Msg3 transmission in the corresponding time slot (or transmissionoccasion), preferably only in the earliest available.

In one example, the base unit may indicate to the UE, or alternativelythe specification may specify the UE, to transmit Msg3 in some (e.g.,see fifth embodiment below) or all indicated time slots or transmissionoccasions in which the clear channel assessment succeeds, withtermination of the Msg3 transmission on reception of ACK for Msg3 or onreception of Msg4 by the UE. This improves the existing solutions,because there is no need for an additional downlink retransmissionrequest.

A fifth embodiment provides for the transmission of Msg3 in severaltransmission opportunities (e.g., time slots). It can be seen as anenhancement of the fourth embodiment, where the difference is that Msg3may be transmitted in more than a single time slot. It can be seen asmultiple HARQ (re)transmissions of the same transport block without theretransmission request feedback loop. According to this embodiment, thebase unit includes a “number of Msg3 transmissions” parameter in Msg2which tells the UE during how many transmission opportunities (e.g.,time slots) the Msg3 is to be transmitted. To minimize the risk oflosing the unlicensed channel to another node in between those timeslots, the time slots are beneficially adjacent in time so thatconsecutive time slots are occupied by Msg3 transmissions. Thisembodiment is particularly beneficial if the signal level of Msg3 duringone time slot is not sufficient for successful detection at the baseunit, and is superior to the existing solution since no additional HARQretransmission requests are necessary.

In a sixth embodiment, the UE starts the contention resolution timer ifthe physical layer indicates that Msg3 has been transmitted, i.e. if theCCA procedure for Msg3 succeeded. This saves unnecessary processingefforts by the UE, because it doesn't have to monitor the downlink forMsg4 or Msg3 retransmission requests.

In various implementations, the sixth embodiment may be realized byspecifying that Once the physical layer indicates that Msg3 istransmitted, the MAC entity shall: start thera-ContentionResolutionTimer and restart thera-ContentionResolutionTimer at each HARQ retransmission in the firstsymbol after the end of the Msg3 transmission if the physical layerindicates that Msg3 is (re-)transmitted; monitor the PDCCH while thera-ContentionResolutionTimer is running regardless of the possibleoccurrence of a measurement gap; if notification of a reception of aPDCCH transmission is received from lower layers; etc.

In a seventh embodiment, a UE receives an indication of the number ofpotential transmission occasions for Msg3 in a DCI carrying DLassignment information for the transmission of Msg2. For example, DCIformat 1_0 with CRC scrambled by RA-RNTI, used to assign resources forthe transmission of Msg2, has currently 16 reserved bits, and some orall of the reserved bits can be used to signal the number of potentialMsg3 transmission occasions. The number of potential Msg3 transmissionoccasions may be configured differently and signaled separately (withdifferent bit fields) for each detected preamble, or alternatively maybe set to be common for all detected preambles and signaled with acommon bit field. This can save resources in the Msg2 payload, as thecorresponding information is contained in the DCI, and the DCI size isnot modified since only a plurality of currently designated “reserved”bits is changed.

In one example, the UE is configured with a set of number of potentialMsg3 transmission occasions by higher layers (e.g., RRC) and the DCIcarrying DL assignment information for the transmission of Msg2indicates one value from the set the UE should use for determining theindicated Msg3 transmission occasions.

In one example, the UE also receives an indication of an offset or gapvalue between consecutive Msg3 transmission occasions in the DCI fordetermining the indicated Msg3 transmission occasions. The UE may beconfigured with a set of offset or gap value and number of potentialMsg3 transmission occasions pairs by higher layers (e.g., RRC) and theDCI carrying DL Msg2 assignment information indicates one value from theset the UE should use for determining the allowed Msg3 transmissionoccasions.

In one variant, the UE may assume the Msg3 PUSCH time and frequencyresource allocation is the same in all the indicated Msg3 transmissionoccasions. If the clear channel assessment succeeds for any of theindicated time slots (or transmission occasions), the UE performs asingle Msg3 transmission in the corresponding time slot (or transmissionoccasion), preferably only in the earliest available.

In one example, the base unit may indicate to the UE or thespecification may specify the UE to transmit Msg3 in some (e.g., seefifth embodiment) or all indicated time slots or transmission occasionsin which the clear channel assessment succeeds, with termination of theMsg3 transmission on reception of ACK for Msg3 or on reception of Msg4by the UE. This improves the existing solutions, because there is noneed for an additional downlink retransmission request.

In various implementations, the seventh embodiment may be realized byselecting, for example, two bits to indicate the number of potentialMsg3 transmission occasions common to all detected preambles in DCI. Forexample, in addition to frequency domain and time domain resourceassignments, MCS information, and TB scaling, the informationtransmitted by means of the DCI format 1_0 with CRC scrambled by RA-RNTImay include 2 bits indicating the number of potential Msg3 transmissionoccasions, thereby reducing the number of reserved bits to 14 bits.

The above embodiments have been generally described for the case of arandom access procedure based on four steps, however this should not beconstrued as limiting the embodiments and solutions to that case.Specifically, in a random access procedure consisting of only two steps,where the base unit assigns PUSCH resources in Msg2, the embodimentsdescribed for Msg3 can applied to the PUSCH transmission indicated byMsg2 by making necessary alterations while not affecting the main pointat issue.

The above embodiments have been generally described for the case of acontention-based random access procedure (CBRA), however this should notbe construed as limiting the embodiments and solutions to that case.Specifically, in a contention-free random access procedure (CFRA), thebase unit orders a UE to perform the random access procedure byassigning a PRACH preamble by means of a DCI (the so-called RACH order).In such a case, the UE is to respond with that indicated preamble inMsg1, whereupon the base unit assigns regular PUSCH resources in Msg2.Even though the PUSCH resources assigned by Msg2 could be seen as notstrictly being part of the random access procedure, the embodimentsdescribed for Msg3 can applied to the PUSCH transmission indicated byMsg2 in CFRA making necessary alterations while not affecting the mainpoint at issue. For example, when applying the third embodiment to theCFRA case, the UE continues with retransmission(s) of the preamble incase the physical layer is not able to transmit the PUSCH indicated byMsg2 in the indicated occasion(s) e.g. due to failed CCA.

In an eighth embodiment, a DCI (e.g. a so-called RACH order) thatindicates a PRACH preamble to a UE to be used in a random accessprocedure, that DCI additionally includes a parameter indicating thenumber of transmission occasions for the PRACH. Like for Msg3transmission according to above embodiments, also Msg1 (i.e. thepreamble) may be subject to a CCA procedure before the physical layer isallowed to transmit the PRACH. Therefore, particularly the third andfourth embodiments (including variants/alternatives) described for Msg3can be applied to Msg1 making necessary alterations while not affectingthe main point at issue.

FIG. 1 depicts an embodiment of a wireless communication system 100 forefficient RACH behavior, such as for NR-U, according to variousembodiments of the disclosure. In one embodiment, the wirelesscommunication system 100 includes remote units 105 and base units 110.Even though a specific number of remote units 105 and base units 110 aredepicted in FIG. 1, one of skill in the art may recognize that anynumber of remote units 105 and base units 110 may be included in thewireless communication system 100.

In one embodiment, the remote units 105 may include computing devices,such as desktop computers, laptop computers, personal digital assistants(“PDAs”), tablet computers, smart phones, smart televisions (e.g.,televisions connected to the Internet), set-top boxes, game consoles,security systems (including security cameras), vehicle on-boardcomputers, network devices (e.g., routers, switches, modems), aerialvehicles, drones, or the like. In some embodiments, the remote units 105include wearable devices, such as smart watches, fitness bands, opticalhead-mounted displays, or the like. Moreover, the remote units 105 maybe referred to as subscriber units, mobiles, mobile units, mobilestations, users, terminals, mobile terminals, fixed terminals,subscriber stations, UE, user terminals, a device, or by otherterminology used in the art.

In various embodiments, the base units 110 may be distributed over ageographic region. In certain embodiments, a base unit 110 may also bereferred to as a RAN node, an access point, an access terminal, a base,a base station, a Node-B, and eNB, an gNB, a Base unit, a Home Node-B, arelay node, a device, a core network, an aerial server, or by any otherterminology used in the art. In some embodiments, the base units 110 arepart of a radio access network that includes one or more controllerscommunicably coupled to one or more corresponding base units 110. Incertain embodiments, the radio access network is communicably coupled toone or more core networks, which may be coupled to other networks, likethe Internet and public switched telephone networks, among othernetworks. These and other elements of radio access and core networks arenot illustrated but may be known by those having ordinary skill in theart.

In one implementation, the wireless communication system 100 iscompliant with the 3GPP protocol, wherein the base unit 110 transmitsusing an OFDM modulation scheme on the DL and the remote units 105transmit on the UL using a SC-FDMA scheme or an OFDM scheme. In variousembodiments, the wireless communication system 100 may use some otheropen or proprietary communication protocol, for example, WiMAX, amongother protocols. The present disclosure is not intended to be limited tothe implementation of any particular wireless communication systemarchitecture or protocol.

The base units 110 may serve a number of remote units 105 within aserving area, for example, a cell or a cell sector via a wirelesscommunication link. The base units 110 transmit DL communication signalsto serve the remote units 105 in the time, frequency, and/or spatialdomain. The remote units 105 may communicate directly with one or moreof the base units 110 via UL communication signals. In variousembodiments, the DL and UL communication signals are sent overunlicensed spectrum. It should be further noted that although variousembodiments depicted in FIGS. 1-8 may be described in the context ofunlicensed transmission/cell, e.g. NR-U, the embodiments should be alsoapplicable to licensed cells, e.g. NR or LTE.

In various embodiments, the remote unit 105 may synchronize to a cell ofa base unit 110 and receive a system information block indicatingvarious capabilities and parameters of the cell. The remote unit 105later determines to initiate a RACH procedure and sends a RACH Msg1 toinitiate a RACH procedure 115 (e.g., PRACH preamble) to the base unit110. In response, in various embodiments, the base unit 110 may indicate120 parameters that provide efficient RACH behavior such as multipletransmission opportunities for individual message completion, randomaccess response window modifications, reduced backoff continuation ofthe RACH procedure, etc. In some embodiments, the efficient behaviorminimizes one or more delays to successfully complete a random accesswhich may occur in an unmodified RACH procedure, such as for example, asspecified in Release 15. For example, in certain embodiments, the baseunit 110 may send multiple RACH Msg2 (e.g., random access responses) tothe remote unit 105. In circumstances in which one or more initial SuchRACH Msg2 messages are sent by the transmitter of the base station butnot received by the receiver of the remote unit due to interference orpoor reception, such efficient behavior may prevent a delay associatedwith having to wait for a random access window to expire beforecontinuing the RACH procedure with selecting and transmitting a PRACHpreamble. Additionally, the remote unit 105 and base unit 110 mayminimize a RACH procedure delay utilizing the efficient RACH behaviordescribed herein.

FIG. 2 depicts one embodiment of a user equipment apparatus 200 that maybe used for may be used for efficient RACH behavior, such as for NR-U,according to embodiments of the disclosure. The user equipment apparatus200 may be one embodiment of the remote unit 105 or UE, described above.Furthermore, the user equipment apparatus 200 may include a processor205, a memory 210, an input device 215, an output device 220, and atransceiver 225. In various embodiments, the transceiver 225 includes atransmitter 230, a receiver 235, and a network interface 240. In someembodiments, the input device 215 and the output device 220 are combinedinto a single device, such as a touchscreen. In certain embodiments, theuser equipment apparatus 200 may not include any input device 215 and/oroutput device 220. In various embodiments, the user equipment apparatus200 may include one or more of the processor 205, the memory 210, andthe transceiver 225, and may not include the input device 215 and/or theoutput device 220.

The processor 205, in one embodiment, may include any known controllercapable of executing computer-readable instructions and/or capable ofperforming logical operations. For example, the processor 205 may be amicrocontroller, a microprocessor, a central processing unit (“CPU”), agraphics processing unit (“GPU”), an auxiliary processing unit, a fieldprogrammable gate array (“FPGA”), or similar programmable controller. Insome embodiments, the processor 205 executes instructions stored in thememory 210 to perform the methods and routines described herein. Theprocessor 205 is communicatively coupled to the memory 210, the inputdevice 215, the output device 220, and the transceiver 225.

The memory 210, in one embodiment, is a computer readable storagemedium. In some embodiments, the memory 210 includes volatile computerstorage media. For example, the memory 210 may include a RAM, includingdynamic RAM (“DRAM”), synchronous dynamic RAM (“SDRAM”), and/or staticRAM (“SRAM”). In some embodiments, the memory 210 includes non-volatilecomputer storage media. For example, the memory 210 may include a harddisk drive, a flash memory, or any other suitable non-volatile computerstorage device. In some embodiments, the memory 210 includes bothvolatile and non-volatile computer storage media.

In some embodiments, the memory 210 stores data related to modifying aradio capability. For example, the memory 210 may store parametersindicating RACH message transmission opportunities, backoff valuescaling parameters, and the like. In certain embodiments, the memory 210also stores program code and related data, such as an operating systemor other controller algorithms operating on the remote unit 105.

The input device 215, in one embodiment, may include any known computerinput device including a touch panel, a button, a keyboard, a stylus, amicrophone, or the like. In some embodiments, the input device 215 maybe integrated with the output device 220, for example, as a touchscreenor similar touch-sensitive display. In some embodiments, the inputdevice 215 includes a touchscreen such that text may be input using avirtual keyboard displayed on the touchscreen and/or by handwriting onthe touchscreen. In some embodiments, the input device 215 includes twoor more different devices, such as a keyboard and a touch panel.

The output device 220, in one embodiment, is designed to output visual,audible, and/or haptic signals. In some embodiments, the output device220 includes an electronically controllable display or display devicecapable of outputting visual data to a user. For example, the outputdevice 220 may include, but is not limited to, an LCD display, an LEDdisplay, an OLED display, a projector, or similar display device capableof outputting images, text, or the like to a user. As another,non-limiting, example, the output device 220 may include a wearabledisplay separate from, but communicatively coupled to, the rest of theuser equipment apparatus 200, such as a smart watch, smart glasses, aheads-up display, or the like. Further, the output device 220 may be acomponent of a smart phone, a personal digital assistant, a television,a table computer, a notebook (laptop) computer, a personal computer, avehicle dashboard, or the like.

In certain embodiments, the output device 220 includes one or morespeakers for producing sound. For example, the output device 220 mayproduce an audible alert or notification (e.g., a beep or chime). Insome embodiments, the output device 220 includes one or more hapticdevices for producing vibrations, motion, or other haptic feedback. Insome embodiments, all or portions of the output device 220 may beintegrated with the input device 215. For example, the input device 215and output device 220 may form a touchscreen or similar touch-sensitivedisplay. In other embodiments, the output device 220 may be located nearthe input device 215.

The transceiver 225 includes at least transmitter 230 and at least onereceiver 235. One or more transmitters 230 may be used to provide ULcommunication signals to a base unit 110, such as the UL transmissionsdescribed herein. Similarly, one or more receivers 235 may be used toreceive DL communication signals from the base unit 110, as describedherein. Although only one transmitter 230 and one receiver 235 areillustrated, the user equipment apparatus 200 may have any suitablenumber of transmitters 230 and receivers 235. Further, thetransmitter(s) 230 and the receiver(s) 235 may be any suitable type oftransmitters and receivers. In one embodiment, the transceiver 225includes a first transmitter/receiver pair used to communicate with amobile communication network over licensed radio spectrum and a secondtransmitter/receiver pair used to communicate with a mobilecommunication network over unlicensed radio spectrum.

In certain embodiments, the first transmitter/receiver pair used tocommunicate with a mobile communication network over licensed radiospectrum and the second transmitter/receiver pair used to communicatewith a mobile communication network over unlicensed radio spectrum maybe combined into a single transceiver unit, for example a single chipperforming functions for use with both licensed and unlicensed radiospectrum. In some embodiments, the first transmitter/receiver pair andthe second transmitter/receiver pair may share one or more hardwarecomponents. For example, certain transceivers 225, transmitters 230, andreceivers 235 may be implemented as physically separate components thataccess a shared hardware resource and/or software resource, such as forexample, the network interface 240.

In various embodiments, one or more transmitters 230 and/or one or morereceivers 235 may be implemented and/or integrated into a singlehardware component, such as a multi-transceiver chip, asystem-on-a-chip, an ASIC, or other type of hardware component. Incertain embodiments, one or more transmitters 230 and/or one or morereceivers 235 may be implemented and/or integrated into a multi-chipmodule. In some embodiments, other components such as the networkinterface 240 or other hardware components/circuits may be integratedwith any number of transmitters 230 and/or receivers 235 into a singlechip. In such embodiment, the transmitters 230 and receivers 235 may belogically configured as a transceiver 225 that uses one more commoncontrol signals or as modular transmitters 230 and receivers 235implemented in the same hardware chip or in a multi-chip module.

Referring now to the structures and functions used or performed by theprocessor 205 for enhancing RACH behavior, such as for NR-U, in variousembodiments as described above, the processor 205 controls thetransceiver 225 to send a PRACH preamble to a base unit to start a RACHprocedure. Moreover, the processor 205 may receive a random accessresponse from the base unit during a random access response window. Invarious embodiments, the processor 205 controls the transmitter 230 totransmit a second PRACH preamble in response to being unable to transmita RACH Msg3 within an indicated RACH Msg3 transmission opportunity.

In the description above, certain embodiments are numbered respectivelyas first, second, third, fourth, fifth, six, seventh and eightembodiments. Here, the messages and functions used and performed by theprocessor 205 are described in an alternate order.

As used herein, the term “transmission opportunity” means an opportunityor occasion that is indicated for a base unit and/or a remote unit totransmit a message or other data item and does not necessarily mean thata transmission occurs. In some embodiments, transmission opportunitiesare provided as predetermined time slots and/or a number of occasionsprovided for transmitting.

The third embodiment includes message structures and functions which theprocessor 205 may use to provide efficient RACH behavior by transmittinga second PRACH preamble in response to being unable to transmit a RACHMsg3 indicated RACH Msg3 transmission opportunity.

The fourth and fifth embodiments include messages and functions whichthe processor 205 may use to obtain multiple Msg3 transmissionopportunities and/or multiple Msg3 transmissions where the number oftransmission opportunities and/or Msg3 transmissions is conveyed inMsg2.

The seventh and eighth embodiments are similar to the fourth and fifthembodiments except that instead of the processor 205 receiving aparameter with the number of transmission opportunities and/or thenumber of Msg3 transmissions in Msg2, the parameter with the number oftransmission opportunities and/or Msg3 transmissions is conveyed in DCIcarrying DL assignment information for the reception of Msg2. The eighthembodiment may also apply to the third embodiment, e.g., the parameterwith a number of transmission opportunities and/or Msg1 PRACH Preambletransmissions is conveyed in DCI carrying DL assignment information forthe Msg1 transmission.

The first embodiment includes message structures and functions which theprocessor 205 may monitor for more than one Msg2.

The second embodiment includes message structures and functions whichthe processor 205 may use to modify the behavior of the random accessresponse window.

The sixth embodiment includes structures and functions which theprocessor 205 may use to modify conditions to start thera-ContentionResolution timer and/or to restart thera-ContentionResolution timer.

Referring now in more detail to various embodiments, such as forexample, the embodiment described above as the “third embodiment.” Inone embodiment, the user equipment apparatus 200 includes a transceiver225 that includes a transmitter 230 and a receiver 235. In theembodiment, the transmitter 230 transmits a first PRACH preamble to abase unit to start a RACH procedure. In the embodiment, the receiver 235receives a random access response from the base unit within a randomaccess response window. The user equipment apparatus 200 includes aprocessor 205 that controls the transmitter 230 to transmit a secondPRACH preamble in response to being unable to transmit a RACH Msg3within an indicated RACH Msg3 transmission opportunity.

In various embodiments, the RACH Msg3 comprises a contention request. Insome embodiments, the second PRACH preamble is selected from the samepreamble group as the first PRACH preamble. As explained above, the RACHprocedure is continued with a second PRACH preamble transmission (RACHMsg1), from the same preamble group as the previous preambletransmission, in case the physical layer is not able to transmit Msg3 inthe indicated time slot e.g., in an indicated transmission opportunity.By transmitting the second PRACH preamble in response to the physicallayer indicating that it is not able to transmit Msg3 because the ClearChannel Assessment e.g., listen-before-talk procedure fails, this avoidsa delay associated with the unmodified RACH procedure e.g., of Release15 which waits until the random access window expires before continuingthe RACH procedure with selecting and transmitting a PRACH preamble.

In certain embodiments, the processor 205 considers a contentionresolution timer e.g, ra-ContentionResolutionTimer to be expired inresponse to being unable to transmit the RACH Msg3 within the indicatedRACH Msg3 transmission opportunity. In other words, the RACH procedureproceeds as if the contention resolution timer had expired withouthaving to incur the delay associated with letting it expire according toan unmodified RACH procedure. In some embodiments, being unable totransmit the RACH Msg3 within the indicated RACH Msg3 transmissionopportunity includes failing to successfully perform a clear channelassessment (CCA) e.g., an LBT procedure, for the RACH Msg3. This mayparticularly improve the RACH behavior in an NR-U system since LBTfailures may be one of the more common reasons a message fails to betransmitted in NR-U.

In certain embodiments, the processor 205 considers the RACH procedureas continuing in response to being unable to transmit the RACH Msg3within the indicated RACH Msg3 transmission opportunity. In other words,in response to a CCA/LBT failure, rather than considering the RACHprocedure as not successfully completing within the random accessresponse window, the RACH procedure continues and the processor 205controls the transmitter 230 to transmit a second PRACH preamble.

Of course, as explained above, the user equipment apparatus 200 maysuccessfully transmit RACH Msg1 and may receive a random access response(RACH Msg2) but may fail to successfully transmit a RACH Msg3. Insystems such as NR-U, failure to successfully transmit a RACH Msg3 mayalso be due to a failed CCA/LBT. Rather than waiting for the randomaccess window to expire as in an existing unmodified RACH procedure, invarious embodiments of the efficient RACH behavior, such as for example,the fourth and fifth embodiments described above, the processor 205obtains a plurality of RACH Msg3 transmission opportunities comprisingthe indicated RACH Msg3 transmission opportunity. In variousembodiments, the processor 205 obtains the plurality of RACH Msg3transmission opportunities as communicated in the random access response(RACH Msg2).

In other embodiments, such as the seventh and eighth embodimentsdescribed above, the processor 205 obtains the plurality of RACH Msg3transmission opportunities as communicated in a DCI carrying downlinkassignment information for transmission of the random access response.In various embodiments, the processor 205 controls the transmitter 230to transmit more than one RACH Msg3 in the plurality of RACH Msg3transmission opportunities.

Of course, as explained above, with regard to multiple transmissionopportunities for RACH Msg1 which occurs before RACH Msg2, other messagestructures and functions may be used to convey information about asecond PRACH preamble to be transmitted in response to a failure such asa CCA/LBT failure. In various embodiments, the processor 205 receives aDCI indicating a PRACH preamble to be used in the RACH procedure (“RACHOrder”) and a parameter indicating a predetermined number of RACH Msg3transmission opportunities. In certain embodiments, the processor 205receives a DCI indicating a PRACH preamble to be used in the RACHprocedure (“RACH Order”) and a parameter indicating a predeterminednumber of RACH Msg1 transmission opportunities.

In various embodiments, multiple opportunities for successfullyreceiving a random access response (Msg2) may also be obtained in theefficient RACH behavior. In some embodiments, the processor 205 monitorsfor more than one random access response transmitted within the randomaccess response window. In various embodiments, the processor 205 stopsmonitoring for the more than one random access response in response toperforming a successful clear channel assessment for transmitting theRACH Msg3. In some embodiments, a MAC entity of the user equipmentapparatus 200 considers the RACH procedure as ongoing in response to notbeing able to transmit the RACH Msg3 within an indicated RACH Msg3transmission opportunity for transmitting the RACH Msg3.

Other enhancements to the RACH behavior may further minimize delaysassociated with unmodified RACH behavior that may occur in existingsystems such as Release 15. In certain embodiments, the processor 205controls the transmitter 230 to transmit the second PRACH preamble usinga reduced backoff value in response to being unable to transmit the RACHMsg3 within the indicated RACH Msg3 transmission opportunity. In someembodiments, the reduced backoff value overrides a backoff valueindicated in the random access response. In various embodiments, thereduced backoff value is obtained by applying a scaling factor to thebackoff value indicated in the random access response. In variousembodiments, the scaling factor applied to the backoff values is ascaling parameter for a backoff indicator (e.g., such as the scalingfactor for the backoff indicator (BI) scalingFactorBI parameter) forprioritizing transmission of the first PRACH preamble.

In certain embodiments, the processor 205 continues monitoring for aPhysical Downlink Control Channel (“PDCCH”) requesting retransmission ofthe RACH Msg3, the PDCCH addressed to an identifier selected from a CellRadio Network Temporary Identifier (“C-RNTI”) and a Temporary Cell RadioNetwork Temporary Identifier (“TC-RNTI”).

In some embodiments, in response to not being able to transmit the RACHMsg3 in the indicated RACH Msg3 transmission opportunity, the processor205 further continues monitoring for a Physical Downlink Control Channel(“PDCCH”) requesting retransmission of the RACH Msg3, the PDCCHaddressed to an identifier selected from a Cell Radio Network TemporaryIdentifier (“C-RNTI”) and a Temporary Cell Radio Network TemporaryIdentifier (“TC-RNTI”) while performing a transmission of the secondPRACH preamble.

In some embodiments, such as the third embodiment described above, thecontention resolution timer ra-ContentionResolutionTimer, started whenthe MAC PDU containing Msg3 was delivered from MAC layer to PHY layerfor transmission, may be still running while the user equipmentapparatus 200 is transmitting the first or second PRACH preamble. Inembodiments in which the receiver 235 of the user equipment apparatus200 receives a PDCCH requesting a retransmission of Msg3, the processor205 may stop further transmission(s) of the PRACH preamble andpotentially related monitoring for a corresponding RAR. In response toreceiving a PDCCH requesting retransmission of the RACH Msg3, theprocessor 205 may stop further transmissions of the second PRACHpreamble and accordingly may also stop monitoring for a correspondingrandom access request.

In certain embodiments, such as the sixth embodiment described above, inresponse to performing a successful clear channel assessment for theRACH Msg3, the processor 205 starts a contention resolution timer. Asexplained above, this saves unnecessary processing efforts by the userequipment apparatus 200, since the processor 205 doesn't have to monitorthe downlink for Msg4 or Msg3 retransmission requests.

In some embodiments, in response to successfully receiving a randomaccess response for the second PRACH preamble, the processor 205 stopsthe contention resolution timer and controls the transmitter 230 totransmit the RACH Msg3 according to the received random access response.

Referring now in more detail to the fourth and fifth embodiments whichobtain multiple transmission opportunities for the user equipmentapparatus 200 to transmit the contention request (or other RACH Msg3).In certain embodiments, such as the fourth embodiment described above,minimizing the delay includes obtaining a plurality of transmissionopportunities to transmit a contention request (or other RACH Msg3)during the random access response window. In some embodiments, theprocessor 205 continues the RACH procedure with selecting andtransmitting a PRACH preamble in response to being unable to transmitthe contention request (or other RACH Msg3) during the random accessresponse window.

In various embodiments, the receiver 235 receives a predetermined numberfor the plurality of transmission opportunities in which the userequipment apparatus 200 may transmit the contention request (or otherRACH Msg3) and communicates the predetermined number to the processor205. In some embodiments, the predetermined number is received in therandom access response which is also referred to herein as a Msg2 and/oran RAR.

In one embodiment, the processor 205 determines a MAC payload size forthe random access response based on the predetermined number. Asexplained above, the uplink grant field of the MAC payload for randomaccess response (RAR) may include one or more Msg3 PUSCH time resourceallocation fields (e.g., multiples of four bits). The user equipmentapparatus 200 determines the size of the MAC RAR, based on the indicatedor predetermined number of potential Msg3 transmission occasionsreceived by the processor 205, which in some embodiments, is received inthe RAR. Since the MAC PDU consists of a MAC header and one or more MACrandom-access responses, the MAC payload size, in such embodiments,equals the size of each MAC RAR times the predetermined number oftransmission opportunities received by the processor 205 e.g., in therandom-access response.

In various embodiments, the transmission opportunities are distributedaccording to a time slot pattern received in the random-access responsemessage. In other words, as explained above, in such embodiments, Msg2can indicate a time slot or transmission opportunity pattern duringwhich the Msg3 transmissions are authorized.

It may be noted that as used herein, that while the receiver 235 of theuser equipment apparatus 200 receives RF data transmitted by atransmitter of a base station, the processor 205 receives the contentand/or values within the RF data received by the receiver 235 and maytake actions in response to receiving such content and/or values.Likewise, when data is transmitted by the transmitter 230 of the userequipment apparatus 200, the receiver 335 of the base unit 110 receivesthe RF data transmitted by the user equipment apparatus 200 and aprocessor of the base unit 110 receives the content and/or values withinthe RF data received by a receiver of the base unit 110.

In some embodiments, the processor 205 receives the predetermined numberof transmission opportunities for transmitting the contention requestvia a mode other than in the random-access response. For example, incertain embodiments, the processor 205 receives the predetermined numberof transmission opportunities for transmitting the contention requestvia broadcast system information.

In other embodiments, the processor 205 receives the predeterminednumber of transmission opportunities for transmitting the contentionrequest via higher level signaling. As used herein, the term “higherlayer signaling” may be used to refer to layers above the PHY layer(according to the OSI model), include the MAC layer (e.g. MAC CE), RRClayer, and further layers above, and their corresponding signals andmessages, unless otherwise clear from context.

In further embodiments, the processor 205 receives the predeterminednumber of transmission opportunities for transmitting the contentionrequest based on the predetermined number been established in aspecification for a particular Release, where the term “Release” mayrefer to a 3GPP implementation of features at a given point in time. Incertain embodiments, the processor 205 applies a contention requestphysical uplink shared channel (PUSCH) time and frequency allocationthat is the same for the plurality of transmission opportunities. Suchembodiments help to save time and minimize delay while ensuring properfunction by avoiding the need to determine PUSCH time and frequencyallocations for each of the plurality of transmission opportunities.

In various embodiments, the processor 205 causes the transmitter 230 totransmit a single contention request at an at an earliest transmissionopportunity for which a clear channel assessment is successful. As usedherein, the term “clear channel assessment” may also be referred to as alisten-before-talk (“LBT”) procedure. In other words, as explainedabove, if the physical layer indicates that Msg3 has been transmitted(e.g., after the clear channel assessment succeeds) for any of theindicated time slots (or transmission opportunities), the UE performs asingle Msg3 transmission in the corresponding time slot (or transmissionopportunity), for example, in the earliest available transmissionopportunity (e.g., the earliest transmission opportunity for which aclear channel assessment is successful).

In certain embodiments, the processor 205 causes the transmitter 230 totransmit the contention request in any of the plurality of transmissionopportunities for which a successful clear channel assessment isperformed.

In some embodiments, the processor 205 causes the transmitter 230 not totransmit an additional contention Msg3 in response to receiving one of:an acknowledgement for the contention request and a contentionresolution message. In other words, the processor 205 terminates furtherMsg3 transmission opportunities on reception of ACK for Msg3 or onreception of a contention or a message (Msg4) by the UE. This improvesthe provides an improvement over the existing solutions, since there isno need for an additional downlink retransmission request, thus helpingthe user equipment apparatus 200 minimize RACH procedure delay that mayoccur in RACH procedures, such as provided in Release 15.

Referring now to the “fifth embodiment” described above, in certainembodiments, the processor 205 controls the transmitter 230 to transmita plurality of contention requests corresponding to the plurality oftransmission opportunities. The fifth embodiment is similar to thefourth embodiment with the additional feature that multiple Msg3 may betransmitted rather than transmitting one Msg3 in one of multipletransmission opportunities as described e in the fourth. Thus, the fifthembodiment may be seen as an enhancement of the fourth embodiment, wherea difference between the fifth embodiment and the fourth embodiment isthat Msg3 may be transmitted in more than a single time slot. It mayfurther be seen as effectively performing the function of multiple HARQretransmissions of the same transport block without incurring the delayassociated with the HARQ retransmission request feedback loop. In suchembodiments, the processor 205 may receive a predetermined number ofcontention requests to transmit.

In certain embodiments, to minimize the risk of losing an unlicensedchannel to another node in between time slots, the transmissionopportunities may include multiple adjacent time slots so thatconsecutive time slots are occupied by Msg3 transmissions. Thisembodiment is particularly beneficial if the signal level of Msg3 duringone time slot is not sufficient for successful detection at the baseunit, and is superior to the existing solution since no additional HARQretransmission requests are necessary.

In some embodiments, the processor 205 causes the transmitter 230 totransmit the contention requests in more than one of the plurality oftransmission opportunities in response to performing a successful clearchannel assessment for the more than one transmission opportunities.

Furthermore, in various embodiments, the processor 205 may cause thetransmitter 230 to transmit the contention requests in more than one ofthe plurality of transmission opportunities in response to performing asuccessful clear channel assessment i.e., a successful LBT procedure forthe more than one transmission opportunities. In other words, once thephysical layer indicates that the transmitter 230 has transmitted thecontention request, additional contention requests may be transmitted inother transmission opportunities without waiting to determine whetherthe transmitted contention request has been received by the base unit110.

Referring now to the seventh and eighth embodiments which also includestructures and functions which the processor 205 may use to minimizeRACH procedure delay that may occur in systems using unmodified RACHprocedures where the delay is related to Msg3 failure such as failure togain channel access due to a CCA/LBT failure. In many respects, theseventh embodiment described above is similar to the fourth and fifthembodiments also described above with one difference being that the inthe seventh embodiment, instead of conveying information about thenumber of transmission opportunities in the random-access responsemessage (Msg3) information about the number of transmissionopportunities is conveyed in the DCI carrying downlink information.

For example, in certain embodiments, multiple Msg3 transmissionopportunities are supported and conveyed to the user equipment apparatus200 in the DCI carrying downlink assignment information rather than inMsg2, the random-access response as described above with respect to thefourth and fifth embodiments.

For example, in some embodiments, the processor 205 receives thepredetermined number for the plurality of transmission opportunities inwhich the user equipment apparatus 200 may transmit the contentionrequest includes receiving downlink control information (“DCI)”indicating the predetermined number of transmission opportunities fortransmitting a contention request during the random-access responsewindow. For example, DCI format 1_0 with CRC scrambled by RA-RNTI, usedto assign resources for the transmission of Msg2, has currently 16reserved bits, and some or all of the reserved bits can be used tosignal the number of potential Msg3 transmission occasions.

In certain embodiments, the number of potential Msg3 transmissionoccasions may be configured differently and signaled separately (withdifferent bit fields) for each detected preamble, or alternatively maybe set to be common for all detected preambles and signaled with acommon bit field. This can save resources in the Msg2 payload, as thecorresponding information is contained in the DCI, and the DCI size isnot modified since only a plurality of currently designated “reserved”bits is changed.

In certain embodiments, the parameter indicating the predeterminednumber of transmission opportunities is encoded within two bits of theDCI and is configurable for each detected PRACH preamble. Alternatively,in some embodiments, the predetermined number of transmissionopportunities may be set to be common for all detected preambles andsignaled with a common bit field. This can save resources in the Msg2payload, as the corresponding information is contained in the DCI, andthe DCI size is not modified since only a plurality of currentlydesignated “reserved” bits is changed. For example, in Release 15, twoof the 16 reserved bits may be used for encoding the number of potentialMsg3 transmission opportunities.

In various embodiments, the processor 205 receives a configurationcomprising a set of candidate numbers of potential transmissionopportunities for transmitting the contention request, where theparameter indicates a particular one of the set of candidate numbers ofpotential transmission opportunities for transmitting the contentionrequest. In one example, the user equipment apparatus 200 receives a setof numbers of potential Msg3 transmission occasions conveyed by higherlayer signaling (e.g., RRC) and the DCI carrying DL assignmentinformation for the transmission of Msg2 indicates one value from theset the UE should use for determining the indicated Msg3 transmissionoccasions. By way of illustration, in one example, two bits may be usedto select any of four numbers (e.g., 2, 4, 8, 16) from within a set ofpossible transmission opportunities where binary sequence “00” mayindicate two transmission opportunities, “01” may indicate fourtransmission opportunities, “10” may indicate eight transmissionopportunities, and “11” may indicate sixteen transmission opportunities.

In certain embodiments, the processor 205 receives via the DCI, anoffset value between consecutive transmission opportunities for thecontention request. In other words, the user equipment apparatus 200receives an indication of an offset or gap value between consecutiveMsg3 transmission occasions in the DCI for determining the indicatedMsg3 transmission occasions. The user equipment apparatus 200 may beconfigured with a set of offset or gap value and number of potentialMsg3 transmission opportunities by higher layer signaling (e.g., RRC)and the DCI carrying DL assignment information for the transmission ofMsg2 assignment information indicates one value from the set which theuser equipment apparatus 200 should use for determining the indicatedMsg3 transmission occasions.

In some embodiments, the processor 205 applies the same contentionrequest PUSCH time and the same frequency allocation for the pluralityof opportunities. In various embodiments, the processor 205 causes thetransmitter 230 to transmit a single contention request within theplurality of transmission opportunities, the single contention requestbeing transmitted at an earliest opportunity of the transmissionopportunities for which a clear channel assessment is successful.

In various embodiments, the processor 205 causes the transmitter 230 tonot transmit an additional contention request in response to receivingone of an acknowledgement for the contention request and a contentionresolution message. In some embodiments, the processor 205 receives apredetermined number of contention requests to transmit. In someembodiments, the transmission opportunities include consecutive adjacenttime slots.

For example, in certain embodiments, the processor 205 causes thetransmitter to transmit contention requests in more than one of theplurality of transmission opportunities in response to performing asuccessful clear channel assessment for the more than one transmissionopportunities.

Referring now to the eighth embodiment described above, the eighthembodiment supports assigning multiple transmission opportunities by asingle PDCCH order also sometimes referred as a RACH order. The DCIproceeding the transmission of a PRACH preamble (Msg1) starts the RACHprocedure so at the time the DCI is received there is no ongoing RACHprocedure. In some embodiments, such as for example the eighthembodiment described above, minimizing the delay includes receiving in aDCI indicating the PRACH preamble to be used during the RACH procedure(“RACH order”), a parameter indicating a predetermined number oftransmission opportunities for transmitting the first PRACH preamble tothe base unit 110.

In other words, in various embodiments, such as variations of the eighthembodiment described above, a DCI such as a RACH order indicates a PRACHpreamble to the user equipment apparatus 200 be used in a random-accessprocedure, that DCI additionally includes a parameter indicating thenumber of transmission opportunities for the transmitting the PRACH.Similar to the way that transmission opportunities for Msg3 transmissionmay be subject to a clear channel assessment i.e., an LBT procedurebefore the physical layer may transmit the one or more contentionrequests (Msg3), in embodiments where the user equipment apparatusobtains multiple transmission opportunities to transmit the PRACHpreamble, the processor 205 causes a clear channel assessment to beperformed before transmitting any message to minimize the likelihoodthat the message may interfere with other transmissions e.g., on theunlicensed media. Similarly, the variants and alternative embodimentsthat are described above with respect to the multiple transmissionopportunities for Msg3 may also apply to multiple transmissionopportunities for Msg1 taking into account that the DCI for the RACHOrder should be used for conveyed information about transmitting thesecond PRACH preamble rather than DCI for the Msg3 as explained abovewith respect to embodiments such as the fourth and fifth embodimentsdescribed above.

Referring now to the first embodiment which includes structures andfunctions which the processor 205 may use to enhance RACH behavior andin various embodiments, to minimize RACH procedure delay related to Msg2failure may occur in existing systems using an unmodified RACH procedurewhere the efficient RACH behavior minimizes the delay by monitoring formore than one Msg2. In one embodiment, referred to above as the firstembodiment, the processor 205 of the user equipment apparatus 200minimizes the RACH procedure delay relative to the delay that wouldoccur in unmodified RACH procedures such as for example in Release 15,by monitoring for more than one random-access message during therandom-access response window even after the processor 205 hassuccessfully received a random-access response message containingrandom-access preamble identifiers that match the transmitted PRACHpreamble which is to say after the random-access response reception isconsidered successful. In various embodiments, the processor 205controls the transmitter 230 to transmit contention request (Msg3)during the random-access response window where the contention request issent in response to receiving the random-access response message.

In some embodiments, in order to avoid conflicting or unclear behaviorwith respect to the contention request transmission, the additionalrandom access response indicates the same contention request transportblock size as the random access response. Said another way, the UE mayexpect that multiple Msg2 transmissions indicate the same Msg3 transportblock parameters, such that the transport block size indicated by two ormore Msg2 transmissions within the ra-ResponseWindow does not change.This simplifies the implementation for the user equipment apparatus 200because the same data payload can be kept in the transmission buffer.

The efficient behavior of the user equipment apparatus 200 according tothis first embodiment indicates that the base unit 110 may performmultiple Msg2 transmissions within the same ra-ResponseWindow. From thelack of successful Msg3 reception (e.g., by DTX detection on Msg3 PUSCHresource or associated reference signal corresponding to Msg3), the baseunit 110 cannot know whether the user equipment apparatus 200 wasmissing a Msg2 transmission, or whether channel access was not alloweddue to a failed LBT procedure. According to current specification, incase the user equipment apparatus 200 has missed Msg2 reception, theuser equipment apparatus 200 continues to monitor for PDCCH with CRCscrambled by RA-RNTI throughout the ra-ResponseWindow until it receivesa valid PDCCH with CRC scrambled by RA-RNTI and the Random AccessResponse containing Random Access Preamble identifier that matches thetransmitted PRACH preamble index.

Therefore, the base unit 110 cannot be sure whether a HARQretransmission grant can be interpreted correctly by the user equipmentapparatus 200, as that requires a successful reception of Msg2 addressedto the UE. To facilitate this improvement, the UE is mandated tocontinue monitoring for Random Access Responses (Msg2) for the wholeduration of the ra-ResponseWindow. According to the existingspecification, this implies monitoring downlink control information(DCI) where the CRC parity bits are scrambled with the RA-RNTI.

In certain embodiments, the base unit 110 can send another Msg2 (withthe above-mentioned constraint of keeping the transport block size thesame) to schedule another Msg3 transmission opportunity, instead ofusing a PDCCH carrying DCI triggering a HARQ retransmission of Msg3,where the CRC parity bits of the DCI are scrambled with a Temporary CellRadio Network Temporary Identifier (TC-RNTI) or scrambled with aCell-Radio Network Temporary Identifier (C-RNTI).

In some embodiments, the additional random-access response messageincludes an additional redundancy version (RV) parameter to facilitateefficient HARQ combination of a plurality of contention requesttransmissions.

In various embodiments, the random-access response window that isstarted after receiving the random-access response message is longerthan a release-defined random access response window length. As usedherein, the term “release defined random-access response window length”refers to an RAR window size defined for current release of a 3GPP radiosystem standard. For example, in Release 15, the RAR window size is 10ms and for Release 16, the RAR window size is expected to be extended to20 ms.

In certain embodiments, the RAR window that is started after receivingthe random-access response message is longer than a system frame length.In some embodiments, the system frame length is 10 ms. In variousembodiments the processor 205 computes a random-access radio networktemporary identifier based on a system frame number module low oninteger multiple of the system frame length. In other words, to uniquelyidentify the multiple RACH occasions with the larger (>10 ms)ra-ResponseWindow length, the RA-RNTI computation may need to be updatedand be based on the SFN (System Frame Number). In addition, the RA-RNTImay be based on an integer parameter ‘x’ representing the maximumallowed value of the (extended) Msg2 window (ra-ResponseWindow) (e.g.,in multiple of 10 ms) which may be fixed in the specification (e.g.,x=ceil(max Msg2 window length (in ms)/10), so x=2 for 20 ms maximumvalue of the Msg2 window) or in certain embodiments may be signaled viahigher layers such as in the RACH configuration.

Referring now to the second embodiment which includes structures andfunctions which the processor 205 may use to modify the behavior of therandom access response window which may also minimize RACH proceduredelay associated with unmodified RACH behavior such as found in Release15. In various embodiments, enhancing the RACH behavior includesmonitoring for an additional random access response during the randomaccess response window until a trigger ends the random access responsewindow.

In some embodiments, the trigger includes the user equipment apparatus200 successfully completing a clear channel assessment for transmittinga contention request. In other words, the user equipment apparatus 200may stop monitoring for Random Access Responses (Msg2) as soon as Msg3has been physically transmitted in response to Msg2 within thera-ResponseWindow. In this regard, a transmission implies that CCAsucceeded for Msg3. However, it may not necessarily imply that the baseunit has received the transmission successfully. In this way, if Msg2 isreceived but CCA for Msg3 fails, the user equipment apparatus 200 stillmonitors for later Msg2 transmissions until the ra-ResponseWindow stops.The effect is similar to the first embodiment: the base unit 110 cansend another Msg2 (with the mentioned constraint of the transport blocksize) to schedule another Msg3 opportunity, instead of using a PDCCHcarrying DCI where the CRC is scrambled with C-RNTI/TC-RNTI triggering aHARQ retransmission of Msg3.

In certain embodiments, instead of or in addition to using the physicallayer transmission of Msg3 as a stopping criterion i.e., trigger of thera-ResponseWindow, the trigger includes receiving a layer two (“L2”)acknowledgement by the user equipment apparatus 200. In furtherembodiments, the trigger includes receiving a PDCCH carrying downlinkcontrol information where the CRC is scrambled with a relevant radionetwork temporary identifier requesting a HARQ retransmission of acontention request. In various embodiments, the trigger includesreception of a contention resolution message. In certain embodiments,the additional random access response includes an additional redundancyversion parameter to facilitate efficient HARQ combination of aplurality of contention request transmissions.

Referring now to the sixth embodiment which includes structures andfunctions which the processor 205 may use to modify conditions to startthe ra-ContentionResolution timer to enhance RACH behavior e.g., tominimize RACH procedure delay, and/or to restart thera-ContentionResolution timer.

As described above with respect to the sixth embodiment, in variousembodiments, minimizing the RACH procedure delay relative to the HARQretransmission procedure time includes starting a contention resolutiontimer in response to a physical layer entity of the remote unitindicating transmission of the contention request. In such embodiments,the physical layer entity of the remote unit, e.g., the user equipmentapparatus 200, indicating transmission of the contention requestincludes completing a successful clear channel assessment i.e., LBTprocedure for transmitting a contention request. In one embodiment,starting the contention resolution timer includes pausing, e.g.,holding, the contention resolution timer in response to an unsuccessfulclear channel assessment for a transmission opportunity for transmittingthe contention request.

Thus, the structures and functions implemented by the processor 205 ofthe user equipment apparatus 200 improve the function of the NR-U systemby individually and collectively minimizing RACH procedure delay relatedto various message failures relative to the HARQ retransmissionprocedure time that occurs in existing system in response to certainmessage failures.

FIG. 3 depicts one embodiment of a base station apparatus 300 that maybe used for efficient RACH behavior, such as for NR-U, according toembodiments of the disclosure. In various embodiments, the base stationapparatus 300 includes structures and functions that are complementaryto the structures and functions of the remote unit 105, the userequipment apparatus 200, and the UE 405, described above with respect toFIGS. 1, 2, and 4-7. For example, the base station apparatus 300 maytransmit data which is received by the user equipment apparatus 200 andconversely, the user equipment apparatus 200 may transmit data which isreceived by the base station apparatus 300.

In various embodiments, the structures and functions of the base stationapparatus 300 may be generally used to implement the first, second,third, fourth, fifth, sixth, seventh, eighth embodiments described abovewith respect to the user equipment apparatus 200 with the respectiveroles of the base station apparatus 300 and the user equipment apparatus200 being generally complementary regarding transmitting and receivingdata. For example, the processor 305 of the base station apparatus 300may receive the first PRACH preamble which the processor 205 of the userequipment apparatus 200 controls the transmitter 230 to transmit, andvice versa.

The base station apparatus 300 may be one embodiment of the base unit110 (also sometimes referred to as RAN node or gNB) described above.Furthermore, the base station apparatus 300 may include a processor 305,a memory 310, an input device 315, an output device 320, a transceiver325 (which may include one or more transmitters 330 and one or morereceivers 335), and a network interface 340. In some embodiments, theinput device 315 and the output device 320 are combined into a singledevice, such as a touchscreen. In certain embodiments, the base stationapparatus 300 may not include any input device 315 and/or output device320. In some embodiments, the base station apparatus 300 may include oneor more of the processor 305, the memory 310, the transceiver 325, thetransmitter 330 the receiver 335, and the network interface 340, andwithout necessarily including the input device 315 and/or the outputdevice 320.

The processor 305, in one embodiment, may include any known controllercapable of executing computer-readable instructions and/or capable ofperforming logical operations. For example, the processor 305 may be amicrocontroller, a microprocessor, a central processing unit (“CPU”), agraphics processing unit (“GPU”), an auxiliary processing unit, a fieldprogrammable gate array (“FPGA”), or similar programmable controller. Insome embodiments, the processor 305 executes instructions stored in thememory 310 to perform the methods and routines described herein. Theprocessor 305 is communicatively coupled to the memory 310, the inputdevice 315, the output device 320, and the transceiver 325.

In various embodiments, the processor 305 receives a first PRACHpreamble from a remote unit 105 to start a RACH procedure. Moreover, theprocessor 305 may control the transmitter 330 to transmit a randomaccess response during a random access response window. Further, theprocessor 305 enhances RACH behavior and in various embodiments,minimizes a delay for successfully completing the RACH procedurerelative to delays which may occur in an unmodified RACH procedure, suchas for example as specified in Release 15.

The memory 310, in one embodiment, is a computer readable storagemedium. In some embodiments, the memory 310 includes volatile computerstorage media. For example, the memory 310 may include a RAM, includingdynamic RAM (“DRAM”), synchronous dynamic RAM (“SDRAM”), and/or staticRAM (“SRAM”). In some embodiments, the memory 310 includes non-volatilecomputer storage media. For example, the memory 310 may include a harddisk drive, a flash memory, or any other suitable non-volatile computerstorage device. In some embodiments, the memory 310 includes bothvolatile and non-volatile computer storage media.

In some embodiments, the memory 310 stores data related to modifying aradio capability. For example, the memory 310 may store parametersindicating RACH message transmission opportunities, backoff valuescaling parameters, and the like. In certain embodiments, the memory 310also stores program code and related data, such as an operating systemor other controller algorithms operating on the remote unit 105.

The input device 315, in one embodiment, may include any known computerinput device including a touch panel, a button, a keyboard, a stylus, amicrophone, or the like. In some embodiments, the input device 315 maybe integrated with the output device 320, for example, as a touchscreenor similar touch-sensitive display. In some embodiments, the inputdevice 315 includes a touchscreen such that text may be input using avirtual keyboard displayed on the touchscreen and/or by handwriting onthe touchscreen. In some embodiments, the input device 315 includes twoor more different devices, such as a keyboard and a touch panel.

The output device 320, in one embodiment, is designed to output visual,audible, and/or haptic signals. In some embodiments, the output device320 includes an electronically controllable display or display devicecapable of outputting visual data to a user. For example, the outputdevice 320 may include, but is not limited to, a liquid crystal display(“LCD”), a light emitting diode (“LED”) display, an organic lightemitting diode (“OLED”) display, a projector, or similar display devicecapable of outputting images, text, or the like to a user. As another,non-limiting, example, the output device 320 may include a wearabledisplay separate from, but communicatively coupled to, the rest of thebase station apparatus 300, such as a smart watch, smart glasses, aheads-up display, or the like. Further, the output device 320 may be acomponent of a smart phone, a personal digital assistant, a television,a table computer, a notebook (laptop) computer, a personal computer, avehicle dashboard, or the like.

In certain embodiments, the output device 320 includes one or morespeakers for producing sound. For example, the output device 320 mayproduce an audible alert or notification (e.g., a beep or chime). Insome embodiments, the output device 320 includes one or more hapticdevices for producing vibrations, motion, or other haptic feedback. Insome embodiments, all or portions of the output device 320 may beintegrated with the input device 315. For example, the input device 315and output device 320 may form a touchscreen or similar touch-sensitivedisplay. In other embodiments, the output device 320 may be located nearthe input device 315.

The transceiver 325 includes at least transmitter 330 and at least onereceiver 335. One or more receivers 335 may be used to receive ULcommunication signals from a remote unit 105, such as the ULtransmissions described herein. Similarly, one or more transmitters 330may be used to provide DL communication signals to the remote unit 105,as described herein. Although only one transmitter 330 and one receiver335 are illustrated, the base station apparatus 300 may have anysuitable number of transmitters 330 and receivers 335. Further, thetransmitter(s) 330 and the receiver(s) 335 may be any suitable type oftransmitters and receivers. In one embodiment, the transceiver 325includes a first transmitter/receiver pair used to communicate via thenetwork interface 340 with a mobile communication network over licensedradio spectrum and a second transmitter/receiver pair used tocommunicate with a mobile communication network over unlicensed radiospectrum.

FIG. 4 depicts one embodiment of an interaction 400 including a RACHprocedure 425 between a UE 405 and a RAN node 410 (also referred to, incertain embodiments, as base unit). The RAN node 410 broadcasts a systeminformation block (“SIB”) 415, which the UE 405 receives. The UE 405uses information in the SIB 415 to configure itself for the RACHprocedure 425. The UE 405 then sends a PRACH preamble 420 to start theRACH procedure 425, referred to as Msg1 of the RACH procedure 425. TheRAN node 410 receives the PRACH preamble 420 and sends a Random AccessResponse (“RAR”) 430, referred to as Msg2 of the RACH procedure 425. TheUE listens for the RAR 430 over a Random Access Response window 435(ra-ResponseWindow), as described above. In the RACH procedure 425, theUE 405 sends a contention request 440, referred to as Msg3 of the RACHprocedure 425. One example of a Msg3 is an RRC Connection Request. TheRAN node 410 sends a contention resolution message 445 to the UE 405,referred to as Msg4. Here, the Msg4 may include a C-RNTI for the UE 405.

In various embodiments, the interaction 400 may be efficient byminimizing a delay of the RACH procedure 425 related to a failure of amessage between the UE 405 and RAN node 410. For example, the RAN node410 may indicate that the UE 405 has multiple transmission opportunitiesto transmit Msg3. Some of the various ways in which the RACH behaviormay be efficient and a delay of the RACH procedure 425 which may occurin systems using unmodified RACH procedures may be minimized aredescribed below with respect to FIGS. 5-7 and 8.

FIG. 5 is a block diagram illustrating an embodiment of an interaction500 illustrating one embodiment of an efficient RACH behavior, such asfor NR-U. In one embodiment, the interaction 500 includes a RACHprocedure 425 between the UE 405 and the RAN node 410, according toembodiments of the disclosure. In various embodiments, after receivingan initial RAR 430, the UE 405 continues to monitor, e.g., listen, formore than one RAR 430 during the Random Access Response window 435. Insuch embodiments, one distinction is that the RAN node 410 may sendmultiple RAR 430 to the UE 405, as described above. While the RAR 430 isdepicted as occurring during the first transmission opportunity, inother embodiments the channel may be unavailable during the firsttransmission opportunity, requiring the RAN Node 410 to transmit the RAR430 during a subsequent transmission opportunity.

FIG. 6 is a block diagram illustrating another embodiment of aninteraction 600 in which a RACH behavior is efficient e.g., for NR-U. Inone embodiment, the interaction 600 includes a RACH procedure 425between the UE 405 and the RAN node 410 according to embodiments of thedisclosure. In certain embodiments, the UE 405 starts the RACH procedure425 by sending the PRACH preamble 420 which the RAN node 410 receives.In response to receiving the PRACH preamble, the RAN node 410 sends RAR430 to the UE 405. As described above, in certain embodiments, the UE405 may continue monitoring for more than one Msg2, even after the RARreception is considered successful. This continued monitoring by the UE405 for more than one Msg2 increases the probability that the UE 405receives a valid PDCCH with CRC scrambled by RA-RNTI and the RARcontaining the random access preamble identifier that matches thetransmitted PRACH preamble index.

In various embodiments, as described above with respect to FIG. 2, theUE 405 obtains, e.g., is provided with or receives one or moreparameters indicating, multiple Msg3 transmission opportunities. In someembodiments, the UE 405 receives one or more parameters indicatingmultiple Msg3 transmission opportunities and/or multiple Msg3transmissions where the number of transmission opportunities and/or Msg3transmissions is conveyed in Msg2. In certain embodiments, the UE 405receives one or more parameters indicating multiple Msg3 transmissionopportunities and/or multiple Msg3 transmissions where a parameterindicating the number of transmission opportunities and/or Msg3transmissions is conveyed in DCI carrying DL assignment information forthe reception of Msg2.

FIG. 7 is a block diagram illustrating a further embodiment of aninteraction 700 in which a RACH behavior is efficient, such as for NR-U.In one embodiment, the RAN node 410 sends a RACH order 416 whichincludes a number of Msg1 transmission opportunities 423. The UE 405receives the RACH order 416 and determines 418 the number of Msg1transmission opportunities 423 which have been obtained. The UE 405transmits the first PRACH preamble 420 to start the RACH procedure 425.In some embodiments, the UE 405 transmits the first PRACH preamble 420in a first available opportunity of the number of transmissionopportunities 423 obtained. In various embodiments, in response toreceiving the PRACH preamble 420, the RAN node 410 transmits a RAR 430which the UE 405 receives. The UE 405 then determines 438 the number ofMsg3 transmission opportunities it has obtained via the RAR 430.

In various embodiments, the UE 405 transmits a contention request 440(also referred to as Msg3) to the RAN node 410 in one of the receivednumber of Msg3 transmission opportunities such as for example, at theearliest opportunity. In certain embodiments, the UE 405 transmits asecond PRACH preamble 422 in response to being unable to transmit a RACHMsg3 within an indicated RACH Msg3 transmission opportunity 443.

In response to receiving the contention request 440, the RAN node 410transmits a contention resolution message 445 also referred to as Msg4to the UE 405 and the RACH procedure 425 ends. In various embodiments,the number of Msg1 transmission opportunities 423 and/or Msg3transmission opportunities 443 are obtained via broadcast systeminformation, higher layer signaling, and/or by a predefinedspecification as described above. In certain embodiments, the behaviorof the random access response window 435 is efficient and may minimizeRACH procedure delay relative to delays that may occur in existingsystems, such as for example, as in the RACH procedure specified inRelease 15.

FIG. 8 is a schematic block diagram illustrating one embodiment of amethod 800 for providing efficient RACH behavior e.g., for NR-U. In oneembodiment, the method 800 begins and transmits 805 a first physicalrandom-access channel (“PRACH”) preamble to a base unit to start a RACHprocedure, receives 810 a random access response from the base unitduring a random access response window, and transmits 815 a second PRACHpreamble in response to being unable to transmit a RACH Msg3 within anindicated RACH Msg3 transmission opportunity. In various embodiments,the user equipment apparatus 200 and/or the UE 405 perform one or moreof the steps of the method 800.

An apparatus for a remote unit includes, in one embodiment, atransmitter that transmits a first physical random-access channel(“PRACH”) preamble to a base unit to start a RACH procedure; a receiverthat receives a random access response from the base unit within arandom access response window; and a processor that controls thetransmitter to transmit a second PRACH preamble in response to beingunable to transmit a RACH Msg3 within an indicated RACH Msg3transmission opportunity. In one embodiment, the RACH Msg3 includes acontention request. In various embodiments, the second PRACH preamble isselected from the same preamble group as the first PRACH preamble. Incertain embodiments, the processor considers a contention resolutiontimer to be expired in response to being unable to transmit the RACHMsg3 within the indicated RACH Msg3 transmission opportunity.

In one embodiment, being unable to transmit the RACH Msg3 within theindicated RACH Msg3 transmission opportunity includes failing tosuccessfully perform a clear channel assessment for the RACH Msg3. Insome embodiments, the processor considers the RACH procedure ascontinuing in response to being unable to transmit the RACH Msg3 withinan indicated RACH Msg3 transmission opportunity. In various embodiments,the processor obtains a plurality of RACH Msg3 transmissionopportunities comprising the indicated RACH Msg3 transmissionopportunity In certain embodiments, the processor obtains the pluralityof RACH Msg3 transmission opportunities as communicated in the randomaccess response. In one embodiment, the processor obtains the pluralityof RACH Msg3 transmission opportunities as communicated in a DCIcarrying downlink assignment information for transmission of the randomaccess response.

In various embodiments, the processor controls the transmitter totransmit more than one RACH Msg3 in the plurality of RACH Msg3transmission opportunities. In certain embodiments, processor receives aDCI indicating a PRACH preamble to be used in the RACH procedure (“RACHOrder”) and a parameter indicating a predetermined number of RACH Msg3transmission opportunities. In some embodiments, the predeterminednumber of RACH Msg3 transmission opportunities are distributed accordingto a time slot pattern received in the RACH Order. In one embodiment,the processor receives a DCI indicating a PRACH preamble to be used inthe RACH procedure (“RACH Order”) and a parameter indicating apredetermined number of RACH Msg1 transmission opportunities.

In certain embodiments, the predetermined number of RACH Msg1transmission opportunities are distributed according to a time slotpattern received in the RACH Order. In various embodiments, theprocessor controls the transmitter to transmit the first PRACH preambleat an earliest opportunity of the RACH Msg1 transmission opportunitiesin response to performing a successful clear channel assessment. In oneembodiment, the apparatus further includes transmitting the first PRACHpreamble in any of the predetermined number of RACH Msg1 transmissionopportunities for which a successful clear channel assessment isperformed.

In various embodiments, the processor receives a DCI indicating a PRACHpreamble to be used in the RACH procedure (“RACH Order”) and a parameterindicating a predetermined number of RACH Msg1 transmissionopportunities. In one embodiment, the processor monitors for more thanone random access response transmitted within the random access responsewindow. In certain embodiments, the processor stops monitoring for themore than one random access response in response to a trigger. In oneembodiment, the trigger includes successfully completing a clear channelassessment for transmitting a contention request in various embodiments,the trigger includes receiving a layer two acknowledgement.

In some embodiments, the trigger includes receiving a PDCCH carryingdownlink control information where cyclic redundancy check (“CRC”)parity bits are scrambled with a relevant radio network temporaryidentifier requesting a HARQ retransmission of a contention request. Incertain embodiments, the trigger includes reception of a contentionresolution message. In some embodiments, the processor controls thetransmitter to transmit a contention request during the random accessresponse window, the contention request being sent in response toreceiving the random access response. In certain embodiments, the morethan one random access response indicates the same contention requesttransport block size as the random access response. In variousembodiments, the more than one random access response includes anadditional redundancy version parameter to facilitate efficient HARQcombination of a plurality of contention request transmissions. In oneembodiment, the random access response window that is started afterreceiving the random access response is longer than a release-definedrandom access response window length.

In various embodiments, the random access response window that isstarted after receiving the random access response is longer than asystem frame length. In some embodiments, the system frame length is 10ms. In certain embodiments, the processor computes a random access radionetwork temporary identifier based on a system frame number modulo aninteger multiple of the system frame length. In one embodiment, a MACentity of the remote unit considers the RACH procedure as ongoing inresponse to not being able to transmit the RACH Msg3 within an indicatedRACH Msg3 transmission opportunity for transmitting the RACH Msg3. Insome embodiments, the processor controls the transmitter to transmit thesecond PRACH preamble using a reduced backoff value in response to beingunable to transmit the RACH Msg3 within the indicated RACH Msg3transmission opportunity. In various embodiments, the reduced backoffvalue overrides a backoff value indicated in the random access response.In some embodiments, the reduced backoff value is obtained by applying ascaling factor to the backoff value indicated in the random accessresponse.

In certain embodiments, the scaling factor applied to the backoff valuesis a scaling parameter for a backoff indicator for prioritizingtransmission of the first PRACH preamble. In various embodiments, theprocessor continues monitoring for a Physical Downlink Control Channel(“PDCCH”) requesting retransmission of the RACH Msg3, the PDCCHaddressed to an identifier selected from a Cell Radio Network TemporaryIdentifier (“C-RNTI”) and a Temporary Cell Radio Network TemporaryIdentifier (“TC-RNTI”). In some embodiments, in response to not beingable to transmit the RACH Msg3 is the indicated RACH Msg3 transmissionopportunity, the processor further continues monitoring for a PhysicalDownlink Control Channel (“PDCCH”) requesting retransmission of the RACHMsg3, the PDCCH addressed to an identifier selected from a Cell RadioNetwork Temporary Identifier (“C-RNTI”) and a Temporary Cell RadioNetwork Temporary Identifier (“TC-RNTI”) while performing a transmissionof the second PRACH preamble.

In one embodiment, in response to receiving a PDCCH requestingretransmission of the RACH Msg3, the processor stops furthertransmissions of the second PRACH preamble and stops monitoring for acorresponding random access request. In some embodiments, in response toperforming a successful clear channel assessment for the RACH Msg3, theprocessor starts a contention resolution timer. In certain embodiments,starting the contention resolution timer includes pausing the contentionresolution timer in response to an unsuccessful clear channel assessmentfor a transmission opportunity for transmitting the RACH Msg3. In someembodiments, in response to successfully receiving a random accessresponse for the second PRACH preamble, the processor stops a contentionresolution timer and controls the transmitter to transmit the RACH Msg3according to the received random access response.

A method includes, in one embodiment, transmitting a first physicalrandom-access channel (“PRACH”) preamble to a base unit to start a RACHprocedure; receiving a random access response from the base unit duringa random access response window; and transmitting a second PRACHpreamble in response to being unable to transmit a RACH Msg3 within anindicated RACH Msg3 transmission opportunity. In various embodiments,the RACH Msg3 includes a contention request. In some embodiments, thesecond PRACH preamble is selected from the same preamble group as thefirst PRACH preamble. In certain embodiments, the method considers acontention resolution timer to be expired in response to being unable totransmit the RACH Msg3 within the indicated RACH Msg3 transmissionopportunity. A one embodiment, being unable to transmit the RACH Msg3within the indicated RACH Msg3 transmission opportunity includes failingto successfully perform a clear channel assessment for the RACH Msg3.

In various embodiments, the method considers the RACH procedure ascontinuing in response to being unable to transmit the RACH Msg3 withinthe indicated RACH Msg3 transmission opportunity. In some embodiments,the method obtains a plurality of RACH Msg3 transmission opportunitiescomprising the indicated RACH Msg3 transmission opportunity. In oneembodiment, the method obtains the plurality of RACH Msg3 transmissionopportunities as communicated in the random access response. In certainembodiments, the method obtains the plurality of RACH Msg3 transmissionopportunities as communicated in a DCI carrying downlink assignmentinformation for transmission of the random access response. In variousembodiments, the method transmits more than one RACH Msg3 in theplurality of RACH Msg3 transmission opportunities. In certainembodiments, the method receives a DCI indicating a PRACH preamble to beused in the RACH procedure (“RACH Order”) and a parameter indicating apredetermined number of RACH Msg3 transmission opportunities.

In one embodiment, the predetermined number of RACH Msg3 transmissionopportunities are distributed according to a time slot pattern receivedin the RACH Order. In various embodiments, the method receives a DCIindicating a PRACH preamble to be used in the RACH procedure (“RACHOrder”) and a parameter indicating a predetermined number of RACH Msg1transmission opportunities. In certain embodiments, the predeterminednumber of RACH Msg1 transmission opportunities are distributed accordingto a time slot pattern received in the RACH Order. In one embodiment,the method transmits the first PRACH preamble at an earliest opportunityof the RACH Msg1 transmission opportunities in response to performing asuccessful clear channel assessment.

In certain embodiments, the method further includes transmitting thefirst PRACH preamble in any of the predetermined number of RACH Msg1transmission opportunities for which a successful clear channelassessment is performed. In one embodiment, the method receives a DCIindicating a PRACH preamble to be used in the RACH procedure (“RACHOrder”) and a parameter indicating a predetermined number of RACH Msg1transmission opportunities. In various embodiments, the method monitorsfor more than one random access response transmitted within the randomaccess response window. In some embodiments, the method stops monitoringfor the more than one random access response in response to a trigger.In various embodiments, the trigger includes successfully completing aclear channel assessment for transmitting a contention request.

In some embodiments, the trigger includes receiving a layer twoacknowledgement. In various embodiments, the trigger includes receivinga PDCCH carrying downlink control information where cyclic redundancycheck (“CRC”) parity bits are scrambled with a relevant radio networktemporary identifier requesting a HARQ retransmission of a contentionrequest. In certain embodiments, the trigger includes reception of acontention resolution message. In some embodiments, the method transmitsa contention request during the random access response window, thecontention request being sent in response to receiving the random accessresponse. In one embodiment, the more than one random access responseindicates the same contention request transport block size as the randomaccess response. In various embodiments, the more than one random accessresponse includes an additional redundancy version parameter tofacilitate efficient HARQ combination of a plurality of contentionrequest transmissions.

In certain embodiments, the random access response window that isstarted after receiving the random access response is longer than arelease-defined random access response window length. In variousembodiments, the random access response window that is started afterreceiving the random access response is longer than a system framelength. In some embodiments, the system frame length is 10 ms. Incertain embodiments, the method computes a random access radio networktemporary identifier based on a system frame number modulo an integermultiple of the system frame length.

In various embodiments, a MAC entity of the remote unit considers theRACH procedure as ongoing in response to not being able to transmit theRACH Msg3 within the indicated RACH Msg3 transmission opportunity fortransmitting the RACH Msg3. In some embodiments, the method transmitsthe second PRACH preamble using a reduced backoff value in response tobeing unable to transmit the RACH Msg3 within the indicated RACH Msg3transmission opportunity. In some embodiments, the reduced backoff valueoverrides a backoff value indicated in the random access response.

In various embodiments, the reduced backoff value is obtained byapplying a scaling factor to the backoff value indicated in the randomaccess response. In certain embodiments, the scaling factor applied tothe backoff values is a scaling parameter for a backoff indicator forprioritizing transmission of the first PRACH preamble. In someembodiments, the method continues monitoring for a Physical DownlinkControl Channel (“PDCCH”) requesting retransmission of the RACH Msg3,the PDCCH addressed to an identifier selected from a Cell Radio NetworkTemporary Identifier (“C-RNTI”) and a Temporary Cell Radio NetworkTemporary Identifier (“TC-RNTI”).

In certain embodiments, in response to not being able to transmit theRACH Msg3 is the indicated RACH Msg3 transmission opportunity, themethod continues monitoring for a Physical Downlink Control Channel(“PDCCH”) requesting retransmission of the RACH Msg3, the PDCCHaddressed to an identifier selected from a Cell Radio Network TemporaryIdentifier (“C-RNTI”) and a Temporary Cell Radio Network TemporaryIdentifier (“TC-RNTI”) while performing a transmission of the secondPRACH preamble. In some embodiments, in response to receiving a PDCCHrequesting retransmission of the RACH Msg3, the method stops furthertransmissions of the second PRACH preamble and stops monitoring for acorresponding random access request.

In certain embodiments, in response to performing a successful clearchannel assessment for the RACH Msg3, the method starts a contentionresolution timer. In some embodiments, starting the contentionresolution timer includes pausing the contention resolution timer inresponse to an unsuccessful clear channel assessment for a transmissionopportunity for transmitting the RACH Msg3. In certain embodiment, wherein response to successfully receiving a random access response for thesecond PRACH preamble, the method stops a contention resolution timerand transmits the RACH Msg3 according to the received random accessresponse.

Embodiments may be practiced in other specific forms. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. An apparatus comprising: a transmitter thattransmits a first physical random-access channel (“PRACH”) preamble to abase unit to start a RACH procedure; a receiver that receives a randomaccess response from the base unit within a random access responsewindow; and a processor that controls the transmitter to transmit asecond PRACH preamble in response to being unable to transmit a RACHMsg3 within an indicated RACH Msg3 transmission opportunity.
 2. Theapparatus of claim 1, wherein the RACH Msg3 comprises a contentionrequest.
 3. The apparatus of claim 1, wherein the second PRACH preambleis selected from the same preamble group as the first PRACH preamble. 4.The apparatus of claim 1, wherein the processor considers a contentionresolution timer to be expired in response to being unable to transmitthe RACH Msg3 within the indicated RACH Msg3 transmission opportunity.5. The apparatus of claim 4, wherein being unable to transmit the RACHMsg3 within the indicated RACH Msg3 transmission opportunity comprisesfailing to successfully perform a clear channel assessment for the RACHMsg3.
 6. The apparatus of claim 1, wherein the processor considers theRACH procedure as continuing in response to being unable to transmit theRACH Msg3 within the indicated RACH Msg3 transmission opportunity. 7.The apparatus of claim 1, wherein the processor obtains a plurality ofRACH Msg3 transmission opportunities comprising the indicated RACH Msg3transmission opportunity.
 8. The apparatus of claim 7, wherein theprocessor obtains the plurality of RACH Msg3 transmission opportunitiesas communicated in the random access response.
 9. The apparatus of claim7, wherein the processor obtains the plurality of RACH Msg3 transmissionopportunities as communicated in a DCI carrying downlink assignmentinformation for transmission of the random access response.
 10. Theapparatus of claim 7, wherein the processor controls the transmitter totransmit more than one RACH Msg3 in the plurality of RACH Msg3transmission opportunities.
 11. The apparatus of claim 1, wherein theprocessor receives a DCI indicating a PRACH preamble to be used in theRACH procedure (“RACH Order”) and a parameter indicating a predeterminednumber of RACH Msg3 transmission opportunities.
 12. The apparatus ofclaim 1, wherein the processor receives a DCI indicating a PRACHpreamble to be used in the RACH procedure (“RACH Order”) and a parameterindicating a predetermined number of RACH Msg1 transmissionopportunities.
 13. The apparatus of claim 1, wherein the processormonitors for more than one random access response transmitted within therandom access response window.
 14. The apparatus of claim 13, whereinthe processor stops monitoring for the more than one random accessresponse in response to performing a successful clear channel assessmentfor transmitting the RACH Msg3.
 15. The apparatus of claim 1, wherein aMAC entity of the remote unit considers the RACH procedure as ongoing inresponse to not being able to transmit the RACH Msg3 within theindicated RACH Msg3 transmission opportunity for transmitting the RACHMsg3.
 16. The apparatus of claim 1, wherein the processor controls thetransmitter to transmit the second PRACH preamble using a reducedbackoff value in response to being unable to transmit the RACH Msg3within the indicated RACH Msg3 transmission opportunity.
 17. Theapparatus of claim 16, where the reduced backoff value overrides abackoff value indicated in the random access response.
 18. The apparatusof claim 17, wherein the reduced backoff value is obtained by applying ascaling factor to the backoff value indicated in the random accessresponse.
 19. The apparatus of claim 18, wherein the scaling factorapplied to the backoff values is a scaling parameter for a backoffindicator for prioritizing transmission of the first PRACH preamble. 20.The apparatus of claim 1, wherein the processor continues monitoring fora Physical Downlink Control Channel (“PDCCH”) requesting retransmissionof the RACH Msg3, the PDCCH addressed to an identifier selected from aCell Radio Network Temporary Identifier (“C-RNTI”) and a Temporary CellRadio Network Temporary Identifier (“TC-RNTI”).
 21. The apparatus ofclaim 1, wherein in response to not being able to transmit the RACH Msg3in the indicated RACH Msg3 transmission opportunity, the processorfurther continues monitoring for a Physical Downlink Control Channel(“PDCCH”) requesting retransmission of the RACH Msg3, the PDCCHaddressed to an identifier selected from a Cell Radio Network TemporaryIdentifier (“C-RNTI”) and a Temporary Cell Radio Network TemporaryIdentifier (“TC-RNTI”) while performing a transmission of the secondPRACH preamble.
 22. The apparatus of claim 21, wherein in response toreceiving a PDCCH requesting retransmission of the RACH Msg3, theprocessor stops further transmissions of the second PRACH preamble andstops monitoring for a corresponding random access request.
 23. Theapparatus of claim 1, wherein in response to performing a successfulclear channel assessment for the RACH Msg3, the processor starts acontention resolution timer.
 24. The apparatus of claim 1, wherein inresponse to successfully receiving a random access response for thesecond PRACH preamble, the processor stops a contention resolution timerand controls the transmitter to transmit the RACH Msg3 according to thereceived random access response.
 25. A method comprising: transmitting afirst physical random-access channel (“PRACH”) preamble to a base unitto start a RACH procedure; receiving a random access response from thebase unit during a random access response window; and transmitting asecond PRACH preamble in response to being unable to transmit a RACHMsg3 within an indicated RACH Msg3 transmission opportunity.